Agree that the motherboard and PSU are fine for GTX 570 SLI, even if I wouldn't have recommended that Raidmax PSU.
The only difference between those two cards that I can see is the length of the warranty;
the 012-P3-1573-AR has a "Limited Lifetime warranty with registration within 30 days of purchase"
and the 012-P3-1573-KR has a "3 year limited warranty. Registration is recommended".
A single powerful card is always preferable, but a 670 won't outperform two 570's. Since you only game on one monitor, a 670 will be enough to run just about any game on any settings for a single monitor, so that's what I recommend.
Raidmax is generally considered to be a more budget brand, but they're reliable enough.