i have also been asking myself questions about this as i am looking at buying either a 3000+ (venice) from softghost.com for $122 or the 3700+ (san diego) from zipzoomfly.com for $209. both of these prices include shipping.
i just read a review of the venice vs. san diego issue. it appears that the san diego is the chip whose L2 cache worked more completely. the venice had some of its cache not work, so they disabled half of it (in other words, during the manufacture process, the san diego core is at the upper end of the spectrum/normal statistical curve). furthermore, the san diego is the same core that is used in the athlon 64-FX-55 and 57. however, on the non FX chips, its core multiplier cannot be increased. they probably saved the top 3% performing chips for the FX, because they could handle excessive heat/voltage/abuse (higher quality silicon).
The review also covered overclocking results between the two cores. overclocked from 2Ghz, at 2.6 Ghz for both venice (3200+) and san diego (3500+), gaming FPS rates were approximately the same (doom 3 run at 1280x1024). However, the venice vcore voltage had to be increased by approximately +.2V and the San diego core was able to overclock from 2Ghz to 2.6Ghz without increasing the core voltage. In my opinion this says that the San diego is a hell of a lot more overclockable (will run cooler at higher frequencies). the Venice was probably topping out around its 260Mhz system freq. i think the San diego could be pushed to 360Mhz (with the right mobo (asus) and cooling setup).
this difference in the end would be 2.6Ghz (Venice) and 3.6Ghz (san diego) for a fixed core multiplier between the two at 10x. and in overclocking, i would rather not have to increase the processor voltage. for non-overclocking use, the processors perform approximately the same.