@Starlabs--he's talking about a $200 card and you're talking about the GTX 580. Nobody but you has even mentioned the 5850. The point being, go ahead and make some suggestions, but slow down a bit and read what's ahead of you to make sure that you're helpful. For example, ICY BRIDGE does not exist and IVY BRIDGE is made by Intel, not NVidia or AMD so it probably won't directly affect graphics cards. Besides, Ivy Bridge won't be out until 2012 off of current time charts.
OP...amk-aka-phantom said it well. Either card will do well. The GTX 560Ti is probably more heavy OC capable, based off of what I've heard.
In my experience, Fermi OC's like a beast (25% core, 8% mem) on the GTX 460's and 470's I've tried. My friend's GTX 460 768MB beats a stock GTX 470 after 30 minutes of OC'ing w/ Afterburner (w/ Kombustor & Witcher 2 for stability testing).