The overclock fx with the 7970 should hold over quite well assuming future games utilize more cores, but for cost being u going with the 8320, stick with the amd and the sabertooth should get near 4.5 no problem if the cpu can reach that freq and is a good quality board.
For the cooler im not sure if u can find the true spirit anywhere at least in the US, but the noctua is prob a good choice, reviews show under 60c for a 4.6ghz i5