I don't know about the overclocking bit, but as far as the vid card goes, it really isn't worth the extra $200 in my opinion. You'd be better off selling the 5900 and getting the 9800 Pro, which is just under $300 at Newegg.
http://www.newegg.com/app/View...asp?...property&DEPA=1' ">http://www.newegg.com/app/View...submit=property&DEPA=1
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Intel Core i7 860
ASUS P7P55D-E Pro
Corsair HX650W
Corsair XMS DDR3-1333 (4GB @ 8-8-8-24)
Sapphire Radeon HD 6870
Western Digital VelociRaptor 300GB
Western Digital Caviar Black 1TB