Bike purchase advice: looking for a fast tarmac/gravel bike
This is a potentially complex question, because we don't know exactly what 70% tarmac and 30% light gravel means. Light gravel might mean a dirt or crushed limestone road, or it might mean smaller bits of gravel. A roadie might think of light gravel differently from an MTBer.
Consider the surface
Cyclingtips recently proposed a grading system for gravel. I'm posting the sample photographs and descriptions of two grades that could be classified as light gravel.


Grade 2
Suggested tyre size: 700×28 – 700×35


Dirt roads. The native habitat of our crew in Boulder, where well-made, hard-packed dirt roads offer a road-like experience but without the traffic. A 2WD car will have no problems getting along here; a road bike will be mostly fine but some rutting and looseness will mean that it’s getting a little out of its depth. At times, may be even smoother than bad paved surfaces.


At the rockier end of the dirt road spectrum, you start to approach…



Grade 3
Suggested tyre size: 700×32 – 700×38


Reasonably smooth gravel. Discernible small rocks over a hard-packed surface mean that you’re struggling to pick a line on narrower tyres; a bigger volume tyre allows you to keep your speed up. In wet conditions, there’s a fair bit of muck kicked up from the surface so rim brakes, even if they allow the tyre clearance, might not be ideal.

The types of surfaces that are available depend on where you live and where you want to travel. Also, a rider's experience, preferences, and handling skills might allow them to handle a higher grade of gravel on a more road-oriented bike.
From personal experience, I took my road bike on a ride that had about 40% grade 2 or maybe 2.5 gravel, and the rest tarmac. The bike had nominal 25mm tires, which actually measure a bit over 27mm. It was totally fine. On the sectors with some visible gravel stones, I had to be more careful about picking a line. If there were a significant amount of real grade 3 gravel, that bike would not be my first choice.
Also, rain and mud would have modified my preference. I did one ride later in the that was 70-80% on grade 2-2.5 gravel, but it had snowed some and the roads were muddy. I used my gravel bike, and I know that I would have regretted my road bike.
Indeed, the Belgian Waffle Ride in the US explicitly says this in its FAQ:

The kind of bike you ride will depend on the type of rider you are and how comfortable you are in the dirt and during long races. The uniqueness of the BWR is that it really causes great consternation as to what weapon to bring to the fight. Too much bike and the 90 miles of road will zap you. Too little, and the rocks, sand, gravel and water will make you suffer or flat ...


On race day, you will notice there are road bikes with 25mm tires; plenty of Canyon Ultimates will devour the course from the front. There will be plenty of Canyon Grails, a unique gravel bike that provides clean comfort in any dirty detour. There will also be a lot of cyclocross type bikes, like the Canyon Inflite, where 32mm tires and plenty of clearance make for a speedy steed. Still others will be on the Canyon Endurace, with its endurance-optimized relaxed geometry, enhanced control features and race comfort; this bike is as at home on the road as it is in the gravel. You will even see mountain bikes, like the Canyon Lux, a light, full-suspension XC ATV. What you won’t see are e-bikes, time trail bikes or tandems.

The bike you should ride is the one you are most comfortable on for both road and dirt...
Road and gravel bikes are both evolving
Another complicating factor is that the road and gravel bike markets are evolving. Briefly, endurance and even performance road bikes can accept wider tires. This enables them to take on rougher surfaces. If it matters to you, some aerodynamic wheels are even becoming optimized for wider tires (usually nominal 25-28mm tires, paired with internal widths of 23-25mm). Simultaneously, the gravel market is bifurcating into a road-like sub-market and a more adventure-oriented, MTB-like sub-market.
NB: Any specific bikes mentioned here are simply the ones I've read about recently. They're not an exhaustive list. This biases the list towards bikes that have been reviewed, and the named examples tend to be from major manufacturers, or at least ones that are prominent to me for some reason.
The 2020 Trek Domane is an endurance road bike. However, it can accept 38mm tires, and it even has built-in pseudo-suspension. The 2021 Trek Emonda, which is a semi-aero climbing bike, is officially rated for 28mm tires, but it appears has enough space to fit significantly wider tires than that. The article stated that there was 42mm of lateral space at the narrowest point on the frame between the chainstays, and typically about 5mm clearance is recommended, implying that you could run tires measuring 32mm, perhaps a bit wider if you can accept some risk. The Specialized Venge, an aero road bike, was described as being able to accept a 32mm tire.
On the gravel side, one part of the market offers bikes that are like endurance road bikes with clearance for tires up to about 45mm on 700c wheels. As of 2020, the Trek Checkpoint, 3T Exploro, and Cervelo Aspero would clearly fit in this category. All-road bikes may be a synonym for this type of bike. They basically handle similar to endurance road bikes. This type of handling is more than capable off-road. In my view, especially as an owner of a bike like this, these bikes are less fun to handle on singletrack, i.e. in repeated tight turns, with steep descents, on very rough terrain. I have completed some singletrack loops for fun on my Parlee Chebacco. It was fun just to do them, but they were clearly not that bike's ideal terrain.
Some gravel bikes are taking more design cues from MTBs. I've heard them referred to as adventure bikes. In terms of geometry, this tends to mean longer top tubes, shorter stems, and slacker head angles. These produce much higher trail than road-like gravel bikes. This design improves the bike's stability at high speeds and on loose terrain. It makes bikes descend much more confidently on steep singletrack descents, whereas on my Parlee I felt like I might risk flying over the bars (NB: I didn't). This design also produces a larger amount of wheel flop, which makes the front wheel more willing to accept a steep turn at slow speed (e.g. on singletrack). In terms of other equipment, these bikes can take even wider tires, e.g. 50mm tires on 700c wheels. They also may have more equipment mounting points, which can help for things like carrying bikepacking gear and water.
What might this mean for you?
As stated in the FAQ, we prefer not to make product recommendations. Specific bike models might be discontinued, or they might evolve significantly (e.g. the Specialized Diverge was a road-like gravel bike, but it is evolving towards the MTB side of gravel bikes). Road and gravel bikes might evolve in ways we can't anticipate. You have not stated your preferences in bikes, but even if you had, this might boil down to having to take a test ride.
Given the spread of bikes that you already have, you might want to consider a performance road or endurance road bike. As stated, these perform more than acceptably on tamer off-road surfaces. However, you indicated that you have an MTB background in comments. You might actually prefer a more adventure-oriented gravel bike, as it will handle more similarly to the bikes you are used to. This type of bike will still perform more than adequately on road with slick tires.
One minor thing to consider is the gearing. If you intend to do group road rides, road riders often prefer to have narrower-range cassettes. This enables them to attain their ideal cadence at the group's chosen speed. You might have 50x34 chainrings with a 11-28 or -30 cassette. I have that chainring with a 11-34 cassette on my gravel bike. The gearing is not ideal for cyclocross, and it's ill-suited to singletrack. It's relatively steep gearing for gravel, but it's still acceptable.
A 1x setup will have big jumps between gears, which can be annoying in a group road ride. Smaller front chainrings may not quite be steep enough gearing for group road rides. Again, there may be compromises.