1: GTA V, Destiny 2, battlefield V, Assassin's creed unity are just some titles I tested all of which have lower fps.
destiny 2 went from 100+ to about 30-40, GTA V isn't even playable getting about 20 fps, battlefield V went from 80-90+ to about 40-50, ACU is lower can't remember exactly how much lower but is low for the hardware 50-60
2: Yes
3: it was now it's not didn't make a difference
5:refer to answer 1 but something acceptable for the hardware
Cheers
How ever some games haven't changed like Witcher 3 and csgo