Don't get a 550 get a R7770, same price and slightly more powerful. And newer technology. The 550 won't even last you until late 2013 before needing an upgrade.
You're getting a K CPU so I'm assuming you're going to be overclocking (if not, why are you paying extra for a K?), if you do OC that chip I guarantee you the 550 will bottleneck the 3570k in no more then a years time. If you're going to get a budget video card get at least a R7770, otherwise I recommend downgrading your CPU from a 3570k, maybe get a 3470 non-k, and instead spend the extra doe on a 660 or something. That will keep your rig alive for gaming longer.
The mobo looks good for the reason of having 2 PCIe slots however it's a bit overkill.
If the sole purpose of the machine is for gaming and you aren't going to be doing encoding and photoshopping heavily then you want a balanced system but try to lean more towards the video card side, you're getting more of a cpu then needed compared to getting something higher end then a 550.
