I have a Phenom II X6 1100T and its a lot more venerable than people think. In reality its still almost competitive with AMD's current offerings. So no despite what was said above, it will NOT bottleneck badly.
I also have an 8gb RX 480 and I run all new games at 55-60 fps (or more) without stuttering, lag, etc, ultra settings at 1080p. Games like Hitman, Doom, Battlefield 4 and Hardline, etc. The only game he may see some lagging is with Battlefield 1 or Gears of War 4, and thats only a maybe. Being that the previous BF offerings have no problem on my system and it uses the same game engine I would imagine it can't be too bad.
An OC'd 1055T will be very close in performance to my processor.
ClubSpade12 :
Well, I guess from an HD 7770 would it at least keep it going? Also my friend is wondering if it is possible for a motherboard to eventually not support certain GPUs....
No, PCIe is backwards compatible, as long as PCIe is made motherboards will support it
ClubSpade12 :
Essentially, he has a mini atx mobo with the HD 7770, and a 750w PSU, it should work fine with the 480, yeah?
Yes it will work fine, as I said the above opinions are incorrect, it will play excellently.