I would defiantly go for the 570 over the 560, however I would recommend the 6950 over both in terms of price / performance.
Also, instead of the ASUS take a look at http://www.newegg.ca/Product/Product.aspx?Item=N82E1681...
Great motherboard, more than capable of pushing the i5 to 5GHz and supports SLI / Crossfire.
Asrock WERE a division of ASUS, and hence were required to stay out of the high end board market in order to not interfere with the sales of their parent company.
As they have now split from them, they are selling extremely high quality boards at low prices in order to gain market share and establish themselves as a player in the high end market. You wont find a better board for the money at this time.
That is my only input, looks like a great machine!
Have fun with it.
I'm looking at a similar build w/ a 580 GTX and was considering a 650W powersupply, assuming I would upgrade PSU if/when I decide to try and SLIw/ another. So, for me I thought 650W for one 580 GTX was enough. Why 900+ PSU if not for SLI?