Will rx480 Support pci 2.0?

Yes, PCI-E 3.0 is backwards compatible with PCI-E 2.0. Assuming the new RX480 does not introduce a new variant of PCI that is not backwards compatible; which is very unlikely, then the new lineup of Polaris GPUs should be compatible with 2.0 slots.

When it comes to performance, it is likely that the're will be no difference between which generation you use. This can be observed on this Tom's Hardware thread: http://www.tomshardware.com/answers/id-2438733/pci-backwards-compatible-pci.html

I hope I helped. Have a nice day man.
 
Yes. It will. There is very less difference between PCI-E 2.0 and PCI-E 3.0 which is negligible. In some cases PCI-E 2.0 was faster than PCI-E 3.0 . Therefore, you are good to go.
 


It will work just fine.
I recall a while back where games were tested on PCIe 1,2 and 3.
from what I remember the performance difference was very minimal.

Aha. Here's a link.
https://www.pugetsystems.com/labs/articles/Impact-of-PCI-E-Speed-on-Gaming-Performance-518/.