Looks pretty good, I have that cpu and an r9 270 (a 270x is just a slightly overclocked version of it) and it performs pretty well in the games I've tried it on, on Crysis 2 max settings it gets 50-60fps indoors and 40-50fps outdoors, which is very good.
Some changes I recommend however:
-Change the r9 270x to an r9 270, as I said before the only difference is a slight overclock, only get a 270x if the price difference is >$15
-GET A CPU COOLER! The stock amd coolers tend to be crap, you can't overclock at all, and they're usually noisy as hell. I would recommend a Cooler master Hyper 212 evo, costs not too much, is pretty quiet, and provides solid temps.
-It might be worth getting Windows 7 64 bit instead of Windows 8, since Windows 7 is overall more compatible and is preffered by most gamers.
-Storage! I would recommend going with a hybrid drive instead of a mechanical drive, since they're only a little bit more expensive and deliver a fair bit faster performance. Also, if you have the money, a 120gb ssd would vastly improve performance on anything you put on the ssd, it would cost you about $70 though.
-Motherboard! For your setup a Asus m5a97 R2.0 would work fine, and probably be cheaper, plus has a longer warranty than the Asrock board (3yr vs 1yr). If you want to overclock, get the regular m5a97 R2.0, if you don't, get the m5a97 R2.0 LE, which should be even cheaper.
Apart from that, looks good!