EVGA is a great brand, I'd definitely buy into their products.
One 670 would be cooler and less power hungry than two 570s and it would probably be just as fast. I'd get a single 670 like I said before. In the future get another one if you like and two 670s would definitely be much faster than two 570s.
Don't forget the 670 has more V-RAM too, 2GB vs the 1.28GB the 570s have. Even with two 570s in SLI you'd still have 1.28GB. The 670 would be better at playing future games at higher resolutions than two 570s would.