Conclusion
With a little research and testing I think we were able to defuse this potentially confusing situation. Considering the price differential it seemed like the BFG 6600 GT OC was going to be clearly a faster video card than the ATI X700 Pro but this was not entirely the case.
The 6600 GT OC has the reputation as being the "gamer's choice" among the two but this is probably due to the fact that is can handle a serious overclock and because it is compatible with SLI. The card did well in our review and was able to excel in our synthetic testing and other GPU-intensive appplications, especially ones where core speed is a big factor. This card is a bit overpriced, but this is often the case when the card is made by a higher-end partner, like BFG. If you search around you can find lots of 6600 GTs for closer to $200, which is bargain considering the peformance it offers.
ATI's X700 Pro did surprisingly well in our testing. With all the recent hype about SLI, the 6600 GT has gotten a lot of attention and the X700 has been left in the dust. This card proved itself to be a solid performer- it is a worthy successor to the popular 9600 series, though I think it is relatively a stronger video card.
If you are looking for a solid performing video card in the $200 range either of these would be a great choice. The 6600 GT OC sports higher frequencies and better compatibility but the X700 Pro has extra memory and better performance in certain areas, including Doom 3. Overall, looking at the X700 series vs. the 6600 GT series, if you are looking for a great deal you would probably be happier with the X700 but if you are into overclocking and you want that extra bit of gaming performance you should probably pick up the 6600 GT.