I am currently only able to over clock my CPU to about 3.9Ghz, anything beyond results in a crash. I'm currently using Asus M4A88TD-V EVO motherboard with Cooler Master Hyper 212 Plus CPU cooler. I do plan on upgrading sometime next year but until then I would like to find a way to over clock to at least 4 Ghz. I have heard many people who have easily been able to over clock this CPU to 4Ghz but I am having trouble doing it. Would there be a decent performance increase? What do I need to do to be able to get 4Ghz+?
Also, would I get better in-game performance if I turn off 2 cores?
The most likely reason for your crashes is thermal, the Thubans run on a much hotter 45nm process and 125w TPD so you will need better than air to push a Phenom II x 6 beyond 4ghz-4.2ghz max.
Denebs from what I gather have safe operation perameters around 1.55vCore but the thubans are less probably don't want to be pushing beyond 1.4 that long. I would find your highest clock at under 1.3vCore, just up your CPU/NB to 2200-2400 add voltage to your NB you should have a stable 3.ghz or so overclock and it is more than enough.
Depending on your chip you will be lucking to get beyond 4ghz without stupid voltage and multipliers, you also don't want to raise the HTT to high that will just increase heat.