The only reason many jumped on the whole 680i SLI boards was specifically for SLI and also T1 settings on RAM and further... to be able to run your RAM at whatever speeds you wanted independently from your CPU. However SLI at 2x16 was the major point. If you don't ever plan on going SLI then there would be little reason to get a 680i mobo.
However 680i SLI boards are great IMHO but... you just have to get lucky which might be a consideration to grab another chipset which might be consistently more stable or easier to OC.
My original 680i SLI AR is a gem of a board (knock on wood) and has worked flawlessly for me. Its OC ability now with my new e6850 is amazing. However I know of a few folks personally that have had many issues with this same board and have had to RMA, tweak, fix, apply paste, swap out cards etc etc to get them to perform well.
I have no experience with the P35 or the 965/975 and I can assure you if you look deep enough you will find issue with them all -- which is perfectly normal.
I also found that once I got used to my bios, and learned much of what it can do using various settings, it really works for me. That took time... however there are good walk troughs out there on this. My 939 DFI board was also great but hell that took time to figure out. Hence there is a learning curve will all boards...
Anyhow long story short seems everything is hinting at the new p35. If I had to get a whole new system today I would get a P35 board...