Which should i buy to get the best gaming performance...
-AMD FX 8320 with the R9 270X
-AMD FX 6300 with the R9 280X
FX6300 and a 280x. You'll have additional costs of grabbing a decent motherboard for the 8320. So the 6300 should be a little more agreeable in that sense. And the GPU is far more important in gaming.
Well, if you want to capture video while gaming, an 8xxx series GPU is the way to go, but a 6300 and a 280x will perform fantastic in most games. At one point an 8320 cost almost the same as a 6300, but you couldn't cheap out on the mobo with an 8xxx series CPU.