Personally I think it's silly to buy an OC'd card when you have the ability to do it yourself, the only advantage is buying it OC'd you get some support and warranty from the manufacturer.
With that said if you want to pay $90 more for a 3-4% FPS increase and the increased support the FTW edition but, if you want the better value the go with the plain 670 and play the silicone lottery and overclock it yourself and maybe get the same performance.
http://www.techpowerup.com/reviews/E...ture_2/15.html