Did i make a big mistake?? 650i vs 680i and a Q6600

The 650i will have very little to do with overclocking the CPU outside of matching the RAM. More importantto a CPU overclock is that the EVGA board has 4 phase power instead of 8 which means, in all liklihood, a bigger vdroop and less stable power so it probably will impact the Overclock. Getting to 3.0-3.2 shouldn't be all that hard, though, even with 4 phase.

Not sure about the memory bandwidth on the 650i but you should be OK as long as you don't push it.

The 650i straight has 16 lanes of PCIe available for graphics. That is plenty for an 8800Ultra.

You won't get the highest benches on that board but you should be able to overclock the CPU to 3.0-3.2 or so, get adequate memory bandwidth and run a single 8800 Ultra without a problem. If this is all you care about then you'll be fine and made a good choice.

What is your budget and will this be a benching rig? If you're just interested in good performance in games and such then why send the board back? It's a great buy at under $100. If you're disappointed you can always get another board later, when you have some more money. I have this Asus P5N32-E SLI Plus that uses a hybrid 680i chips coiupled with a 570i as the SB , has 8 phase power and most of the goodies of a 680i at under $180. It overclcoks like a banshee, is very stable and is a great board all the way around. Personally, i have seen to many problems with the 680i to trust it much.