Commuter bike for better performance: less weight, or internal gear-hub?
When you use your bike every day, reliability is as important as weight. 
I use 2 bikes, with a train ride in between. The bike I use at my work town rarely gets maintained. I take it home 2 times each year. The only things I do regularly is pump the tires and lubricate the chain. Even then it keep riding as good as new. The derailer bike I had here before that needed a lot more care.

The things I learned over the past years:


The simpler the better. If the terrain is flat enough to get by with a bike without gears, do so. 80m elevation is on the edge, and depends on your physical condition. If you feel the upper gear on a Nexus 8 is not large enough, you're riding quite fast (35Km/h+) already. I ride a bike with an Alfine 11, and have no problem doing 35 in 8th gear. Another thing is adjusting your style to spin faster (85+RPM), which generally is also better on the knees.
No front shock absorber. The good ones are too expensive, and the other ones too heavy and crap
No V-brakes or cantilever brakes. At least hydraulic rim (Magura) or disc brakes
Mudguard!
A rack to hang bags (I am very happy with bags like this). No backpacks for me.
A IGH is a lot more carefree then a derailer.
being able to shift at red lights is very handy
The lights have to be driven by a dynamo and fixed to the bike (battery lights get empty or forgotten at the worst possible time)
No NuVinci. It is heavy, and you can't shift when stationary


So I would not use either of the bikes you suggested, but something like this or this

I don't have an opinion on chain vs belt. My girlfriend has a bike with a belt, and that tends to stay cleaner then the chain on my bike, but I don't know whether it is worth the extra expense.