I've heard of much more performance gains in regular usage, but either way, he will still probably obtain a higher clock with the opteron, and best case scenario, he can sell his current venice for about $50.00 covering 2/3 of the costs.
Intel C2D e6600 @ 3.6Ghz
BFG 8800GTS 630/1000
Seagate 360GB and 160GB SATA II 7200 RPM
Cooler Master iGreen 500w Power Supply