Just a note for the Q6700 - If you're running a Quad processor, the last time I checked, the Intel chipsets OC'd the FSB the best by a large margin.
(sorry - no links to back it up. I think it was on the xtremesystems forum. I'm not trying to state a fact, rather advice to check a little further if you decide to go Quad over Dual)
The Commando (965) was around 450Mhz+
Some Bad Axe2's (975) got over 400Mhz
The RD600 barely hit 350Mhz
The 680i's struggled to get 320Mhz
Again, note, this is with the Quad cores, not the Duals. As well, BIOS updates can come fast and possibly fix any of these (I was shocked at how low RD600 scored).
- SLI is out for 965 (well, you can sort of run it on the gen 2 boards, but it's not 16x16 - I think it's 16x4?)
- 975 boards do not officially support SLI - although the hacked drivers are not hard to find
- RD600 - again no SLI, but I'm sure hacked drivers will surface someday (and I'm guessing 16x8)
- 680i - the only one to officially support SLI, but also the slowest performer with the Quad core (last I seen). This is not an issue if you get the E6800 though...
Rumors are spreading that the Intel chipsets will soon officially support both Crossfire and SLI - but I'd never buy a computer based off of unconfirmed rumors.
Your budget is insane! If you really have money to burn, check out Tom's review of custom made cases: http://www.tomshardware.com/2007/01/25/making-a-custom-pc-enclosure-with-protocase/