Here is some of the best advice I can give you.
Download Prime95, and play with it. When you get it installed, if you're still not sure how it works, let me know, and I'll try to do up an online guide with screenshots.
That is THE test, that will show you what is *really* going on with your system, and whether it is stable or not. An OC that is not stable will cause you much greif. Intels will take alot. They are known for their stability, but if they are run outside of their max clocks, or too hot, then they can have you pulling your hair out.
Prime95 is not an option...it's a requirement.
Another program that is a must have is MemTest86.
Also what stang suggested...you defintely need to monitor those temps. You could be running 49 in the BIOS and be gaming at 75C!
Ouch!
Another suggested program is called Throttle Watch. You can set it up to monitor while gaming, and it will show you if the CPU is throttling under load.
Throttling is a protective measure to keep the CPU from killing itself. It's not soemthing you want to rely on to save it. I can't prove it, but I've often suspected that some of these dead prescott's died, becasue they were allowed to throttle due to high OC's and temps before much was known about them. You hardly ever see a post about a dead one anymore, but early on, you can look at the older posts on here and see that it happened much more frequently.
Monitoring these things, and keeping them at their lowest temps will keep them performing, and will make them last alot longer.
These new CPU's are powerful, but you have to test and monitor them alot more than you used to. If a HSF gets too much dust in it, the temps can go through the roof.