I'm running an Athlon 2 x4 (overclocked too!) in an M2N-SLI Deluxe, which is an AM2 socketed motherboard. Absolutely stable for 24/7 usage, no cold boot problems. Which is quite nice for no official support for the AM3 processors.
Of course, your mileage might vary. I really don't know how AM3 processors run in AM2 socketed boards aside from mine.