Its basically all in the title.
I'm thinking of buying the r9 270 and take advantage of the new Mantle API that AMD is going to release. I've had and old GTX 550ti for a while and was also in need of an upgrade.
Also, will a 500w Corsiar PSU be enough to run it?
-Your i3 is good to about a 270X or 7870 XT. So go for it!
-This would be a massive upgrade to your 550 Ti
-Yes a 450w would be enough...