Here is an overclocking guide for Black edition phenom 2's. http://www.overclock.net/t/525113/phenom-ii-overclocking-guide
My X6 1090T tops out at 4.2ghz but I have to pump alot of voltage at it to stay stable. Once I stated OCing my Northbridge and Ram I had to drop the cpu to 4.0ghz to stay stable. By doing this I was able to drop my CPU vcore quite a bit and keep temps in check for 24/7 use under heavy loads on hot days. I now idle at 23 degrees celcius, and under load hit about 50 degrees. The load being a loop of 3dmark 06 cpu test in a loop for about 30 mins. During gaming I never see it go above 46 degrees.
Overall anything above 4.0ghz is not really needed IMO since the voltage to get there won't really cause any huge gains in anything performance wise. Benchmark scores will be slightly higher but FPS in games will only increase a few frames at best, and thats only in CPU intensive games.