Will the Samsung 64GB Evo Plus be sufficient for the Panasonic gx80/85?
What speed does my SD-card need?

The manual states that:



So any card that can continually write 100 Megabit per second (so around 13 MegaByte per second) should be fast enough for recording 4K. For photography, there's no hard number: usually, it's the faster, the better, especially when shooting series of pictures in RAW. However, it will only have influence on the buffer and how fast it is cleared.

Your suggested card has a write speed of up to 60 MegaByte - but "up to" can mean anything in between 0.1 and 60.0 MB/s. Look for benchmarks - or look for 
Speed Classes - those will usually tell you the minimum continuous write speed of a card. Speed-classes come in all sorts of logos and are usually displayed on the card.

Please note that the camera has to support the protocol of the card - A U3 card will only be able to work at C6-speed (at best) in a camera that only supports up to C6.

Now, having a standard is all well and fine - as long as everyone is abiding by it. "Premium" card manufacturers have a reputation to lose, so they usually will not forge speed ratings. If you do not know if you want to trust them, again, you should look for benchmarks and reviews.



Are µSDs more reliable than regular SDs?

No. I carry some of my (non-essential) SD cards in my purse - next to my coins and without protective cases. So I assume that to break an SD-card, you really have to try. SD-cards are usually cheaper than µSD-cards (at same specifications), so I would go with one of these all the time.

This, of course, does not consider cross-device use of the card, e.g. in a smartphone.



Are Samsung's cards reliable?

Simply look for reviews in the internet (e.g. in the link you posted from Amazon). I have no experience with Samsung, though they tend to have good reputation. Their SSDs are always well-received, so I would think the same would go for their SD-cards. However, there is always the possibility that you get the one bad card of a batch - or that one specific model comes out faulty.