I have got my 3700+ overclocked to 2.8ghz stable, at 1.45v idle 28 degrees and load 44 degrees, with the stock cooler, anything over 2.9ghz and the voltage is going up a hell of a lot more quicker, so 2.9ghz seems to be the limit for a 3700+, but a stock cooler should be ok, but a better cooler would be better if you want a quiet system.
Also, i ran prime95 for 12 hours and got no errors, but after a couple of months at 2.8ghz/1.45v it starts to show, i started getting random resets, i bumped the voltage up to 1.5 or 1.47v, and those random resets are gone now, and i have not majour temperature differences.
If you have a decent cooler, from what i have seen, you can possibly get the 3700+ up to 3.0ghz, on one site, max stable overclock was 3.2ghz, and unstable was 3.4ghz, but they were using water cooling.
I got my cpu up to 3.0ghz, i managed to load windows, but i soon got a reset when loading anything CPU intensive, maybe a bit more tweaking in the bios and it might of been stable at that, i would of needed a better cooler tho, as i was on 1.6v.
i had to set the HT multiplyer to 3x, and 2/1.66 on the cpu-mem or fsb ratio, cant remember what it was, and set the fsb speed to 254mhz, and i got 2.8ghz.
the 3700+ is performing just as good as an FX 57 when clocked at 2.8ghz, i got 80,000 in aquamark 03, when with stock speed, i got 72,000.
Best overclockers are the opteron cpu's, the 170's are clocked at 2.0ghz and can rach 3.0ghz stable apparently, i think that is also the case for the 144.