This is a perfect example of a HEAD to HEAD to HEAD comparison.. I am facing the exact same choices.. I have 3 kids.. So.. I am building each one of my kids "gaming" computers for Christmas. So I have to buy things, in lots of 3 (3 kids, 3 computers).. I have already purchased 3 Cooler Master Centurion 5 cases, 3 DFI Lanparty UT nF4-D motherboards and this week, I plan on purchasing 3 processors.. Obviously, if I didn't have to cut corners (building 3 computers vs only building 1 computer), I would opt for a dual core.. Well, I just don't have hundreds of extra dollars just laying around so they are getting sub $100 dollar single core processors.
Opteron 146 (single core @ 2.0ghz w/ 1mb L2 Cache)
Athlon 64 3700+ (single core @ 2.2ghz w/ 1mb L2 Cache)
Athlon 64 3800+ (single core @ 2.4ghz w/ 512kb L2 Cache)
Each processor, I'm sure, is capable of being overclocked to 2.5ghz (unless for some freaky reason you are sold a "dud"). The few questions I have is how much should a person expect from overclocking each processor? Is 2.7ghz the "average" overclock from all 3 processors listed above? If not, what are the averages for each processor? How high would you have to overvolt and use extreme cooling solutions to keep each processor stable?
Personally, since I have overclocking in mind for my kids, I want to push the processor a bit, but not "over push" it.. Kids are destructive by nature so I am shooting for a solid 2.5ghz.. Certainly, the 3800+ is appealing because I would only have to overclock it 100mhz to achieve my goal.. A 100mhz overclock is NOTHING! Viola, my goal would be realized.
With that said, if I was able to raise it "only" 300-400mhz over the 2.4ghz level, with little or no voltage increases that would put me in the 2.7-2.8ghz range. I'm sure that would be very possible with the stock AMD HSF. I definately could live with that sort of overclock for everyday use (for my kids).
The San Diego Core 3700+ is also appealing because it has the 1mb L2 Cache. Understandably, the 3700+ vs 3800+ at the same operating frequency (example 2.7ghz), the benchmarks "should" favor the 3700+ slightly, because of the extra L2 Cache. A good question to ask yourself is, DOES IT REALLY HELP? HOW MUCH EXTRA did the 1mb L2 Cache help? Here are a few links for you to draw your own conclusions.. (on the link below, look what they say about the L2 512kb vs 1mb cache on the SiSoft Sandra results.. hmm). Exerpt from Compressorcooling.com benchmarking results.. "In nearly all plays thus the 3800+ Venice wins against 3700+ San Diego."
Also, I found an article about Athlon 64's vs Opterons.. http://www.devx.com/amd/Article/27340
Just my .02 cents..