I normally don't spend too much time in this Forum (time limitations), but I happened to see the subject. I think its OK to put this sort of question (e.g., hardware advice) in the Tech forum, where it has a good chance of being spotted by those it can help & those that might be technically inclined.
If your post is accurate about the Speed ratings and the cache and price differential, then in fact they are not both San Diego. The 3800 is the Venice. If it is a 130nm 3800+ CPU, then it is a Newcastle core.
The key in deciding is in how you will use it. If you run processes like MP3 creation or video editing or DVD compression, then choose the 3800. That's because the core runs at 2400, vs 2200 for the 3700. The dominant feature is speed, not cache size. For other software, the choice is murky, so I will hit some of the tech details.
Both chips are Socket 939 & have 40-bit physical addresses, 48-bit virtual addresses, 16 total 64-bit integer registers, 16 total 128-bit SSE/SSE2/SSE3 registers. And more importantly for gamers, both have a low-latency integrated DDR memory controller which supports PC3200, PC2700, PC2100 or PC1600 DDR SDRAM and unbuffered DIMMs, with up to 6.4 GB/s memory bandwidth. Coupled with HT, you get one 16-bit link up to 2000MHz, which will give up to 8 GB/s HT I/O bandwidth and 14.4 GB/s total processor-to-system bandwidth. This is a good thing in RTW and Battlefield2, etc. Newcastle (Socket 939) and Clawhammer (Socket 754) cores cannot match this.
About cache that you mentioned, both have and on-chip cache with 64KB Level 1 instruction cache and 64KB Level 1 data cache. The difference is that the San Diego has 1MB of Level 2 Cache, but runs at 2200MHz core CPU speed. The Venice (the 3800+) has 512KB Level 2 Cache, and runs almost 10% faster core speed, at 2400 MHz. This is more important in CPU-limited games like RTW, and hence why I would choose it.
Note: Given an option, stay away from the older Clawhammer 3700+ (2.4GHz) and Newcastle 3800+ (you can ID both by the 130nm die process). Also stay away from Dual Core (Manchester) 3800+ (2.0 GHz core) for now.
The next main question to ask yourself is financial. If it is (saving max money), choose the 3700+. If it is not, then choose neither & get the FX57 which is absolutely without peer right now in gaming... but at ~1,000 USD, its pricy. On the other hand, if you can afford the extra quid differential, then get the 3800+
BOTTOM LINE: Based on taking the context of your post, the choice is the 3800+, easily.
In America, today's mail order prices are:
3700+ (2.2GHz, 1MB L2 Cache) San Diego: $221
3800+ (2.4GHz, 512MB L2Cache) Venice: $283
To run your system well, be sure to look at some more technical detail from AMD,
EDIT: Holy handgrenades, I got the 3700 and 3800 reversed in Paragraph #3! Its fixed now!
[This message has been edited by Wartrain (edited 12-10-2005 @ 08:35 PM).]