Ok, Sounds like something I intend to do, except I'd probably be interested in lower budget and gaming. I'll likely to reuse my case, ssd, harddrives, sound card. Maybe i'll keep my 500W FSP BluePower Power supply, but If intend to do CrossfireX with two HD5770 (I'll get them both for about $60 or less) I think I'll likely need stronger power supply
In any case, it's early for predictions due to lack of parts and prices.
One think I do know - I think for me Core I5-2500 is the best value/performance. I don't feel that 4 extra hyper-threaded cores plus, tiny speed bump worth extra $90-100 for the I7-2600