eVGA 6600 GT is the absolute best for OC.
Not from what I've experienced thus far. The 6800GT is true...but I don't know about these 6600GT's.
LeadTek has an awesome stock cooler from what I hear and has been able to have some good OC's generally reaching 600 core and I've read a lot of people getting 1.1GHz and up on the memory.
Thus far my highest OC is
so the OC'ability is kind of in the 'ehhhh' zone for the 6600GT's....it rests about 52C idle and was hitting 80C full load, 87C in a little bit of a hotter room.
Can't wait to get some water cooling goin then I'll cool that core down REAL good like