I used to run the 3800 X2 on the M2N-E, drop your HT to 4, up your FSB to 220, then test the stability with Orthos. If it passes for an hour keep bumping FSB by 5 until it tests unstable, then up vcore voltage one notch and test for stable. At some point in this process upping vcore won't make it stable, at that point up the ram voltage by one notch at a time until it reaches stable.
I think I hit a wall around 250 HT/FSB and called it good. (2.5 Ghz), I've seen them go to 2.8 2.9 with major cooling. Problem is when you get much past 2.5 it gets much harder, taking a lot more time, and very good cpu cooling. Then the M2N-E doesn't have very good voltage control, I'm on my second M2N-E board and both the voltages bounce up and down like a lap dancer. (Not that I'd Know about that
If you do look at going over 2.5 other voltages have to go up (at least on mine). So if you hit 2.5 stable and want to go higher try bumping up the other available voltages. Probably won't get higher than 2.5 because the memory voltage on that board only go to 1.9 or 1.95v. When you run out of juice for the ram your pretty much done.