I think that might be your overheating problem. Unless you do the overclocking in the bios manually, any AI programs or auto overclocking will up the voltage more than you need it. In some cases, I have seen these programs increase the voltage too much for the processor to handle. That could equate to a lot of heat.
Anyway, the Q9550 is a much better gaming CPU and even a very good match for some of the icore series processors. The 12mb of L3 cache makes a huge difference in a lot of games. It certainly edges out the phenom II. Scroll down for the gaming benchmarks. Note that they use a GTX280 for their testing:
http://www.anandtech.com/bench/Product/50?vs=146
The phenom IIx4 at 3.4GHz:
http://www.anandtech.com/bench/Product/50?vs=102
Your CPU vs a core i7 at a slightly higher clockspeed:
http://www.anandtech.com/bench/Product/50?vs=46
As you can see, you are a match, slightly worse, or slightly better, than even current higher end gaming CPUs.