the x700 series are not very overclockable.... 6600 gt is better than a x700 XT, pro, etc...and has a high potential in OC.
Whatever.
The X700XT (since you brought it up) is faster than the GF6600GT in the same ratio as the GF6600GT is faster than the X700Pro. It's a moot point since the number of XTs ever made/shipped is about equal to that of the GTX-512 at MSRP.
As for overclockability, that all depends on the card you get, and when it comes down to it you recommend and buy on stock performance, and hope for overclock. For all the people who've gotten good overclocks like myself, there are just as many who have trouble going above stock.
The GF6600GT outperforms the X700Pro in most situations (although not all) , and what hurts this particular X700Pro being considered is that it is 128MB as well, so the small additional number of times where the X700Pro benifited from it's 256MB of memory is wipped out here.
The GF6600GT is the clear winner, but don't start telling prokie pies! :roll: