ASUS P8P67 isn't suitable for SLI/Crossfire, you need the P8P67-PRO or equivalent.
The i5-2500k has pretty much the same performance as the i7 for games, the i7 is more for heavy rendering/editing etc.
I would go with air cooling unless you really want to try liquid cooling. You can generally get similar results at the same price and it's safer. Scythe, Noctua and Cooler Master are some good brands to look at.
Just so you know, flashing the bios in a 6950 doesnt always work, its not guaranteed.
I second jmsellars. I will point out that the 6950's you have are not reference design, meaning they will most likely not have the dual bios switch, which aids in flashing the bios. Try and get reference design 6950's.
I understand the 6950's are not a guaranteed flash, it would just be something to try. I can always upgrade cards later as prices fall and games begin to properly support Quad GPUs. I do have a question regarding the HDD's though; Any thoughts on SSD vs Sata II 10k RPM? I have read some reviews of SSD and it seems when they work they are great but it also appears that people tend to have a lot of issues with them working or staying alive longer than 6-8 months.
I should also note that the P8P67 is the DELUXE Edition, I forgot to add that when making the list.
Most of the time (90%) a reference design 6950 2GB can be sucessfully flashed. Therefor, I encourage you to go for it!
The issues pointed out for SSD's are with the 32nm design I believe, so if you get a 34nm ssd you should be ok. But if it was me I would get 2 Spinpoint f3's and put them in raid 0, 2tb of super fast storage for the price of a 100gb 10k drive.
I am thinking about just spending the extra cash and buying 2x 6970's and slightly overclocking them. Things I have read said the 34nm SSD's where recalled so I think I will stick with my VelociRaptors. Never played with RAID or Liquid Cooling but I have always wanted too.
Another question I have concerning CPU. Core i7 2600k vs i7 970, any thoughts on this? I have been looking at several other peoples builds and they seemed to have gone with the 970 and I am unsure as to why, from what I have been reading it seems the 2600k with its Sandy Bridge technology would be the best way to go. I know I can drop down to the i5 and have just as much fun, the i7 choice is more to please my nerd ego than anything else.
The i7-2600k and the i5-2500k are the exact same processor, except the 2600k has Hyper threading. Hyper threading is only used in extremely processor intensive tasks, such as 3D rendering or modeling. You would be better off with the 2500k, as it performs just as well as the i7 in gaming. As for 970 vs 2500k, the 2500k uses a newer design, allowing it to be upgradeable in the future. The 970 uses the LGA 1366, which is an outdated design. Many benchmarks show the 2500k outperforming the 970, even beating the 980x in some games.
So, 2500k is the way to go without a doubt.
NOTE: I would suggest just getting reference design 6950's, as you have a very high likelyhood of being able to unlock.