The San Diego and Venice core has only a $30 difference separating them with the San Diego core costing more (around $234). That's is way good and I would get the San Deigo 3700+ instead. If it was like $100 difference between the two, then forget it. Two similar CPU's shouldn't cost that much and in this case, you pay an extra $30 more to get a better CPU.
AMD Athlon 64 3700+ San Diego 1GHz FSB 1MB L2 Cache Socket 939 Processor - Retail
in comparison to the 3500+ Venice:
AMD Athlon 64 3500+ Venice 1GHz FSB 512KB L2 Cache Socket 939 Processor - Retail
That San Diego core's got some monstrous reviews and very positive. All positive except for the busted contents during shipping on one of them. Have no clue what happened there.