When i started i got my Phenom II x6 1065t stock at 2.9ghz to 3.7ghz on stock. Temps when gaming were 45-55*C would hit 60+ with prime 95 running.
I have a Phenom II x6 1065t stock at 2.9ghz currently OC'd to 4.052 (was 4.102 for months but suddenly became unreliable) @ 1.4875v
You will need a really good cooler, I'm using the Cooler Master v6 and it's an awesome heat sink.
After that you need a good mother board with good cooling on the north and south bridges.
I did my CPU OC first which alot of people don't apparently and then i tuned my other components up. IMO take your time and increase in small incriments and stress test the hell out of it with prime 95 and the games you want to play.
Most important thing is keeping an eye on temperatures because any temp over 65*C will kill a phenom II CPU quickly and voltages over 1.55 I believe will as well.
FWIW when I had my 4.102ghz OC the voltage was 1.51250 and it was stable for months before what I guess is some damage happened and it became unstable.