My mums northwood has been going at 65C load for about a year now.
I would try and take it to about 1.6V and then check your temps. If there abotu 55C then you can start increasing the FSB until you get unstable, try and keep the temps under 60C if you can.
If you have an aircon, take of your case side and put your computer right up next to the airocn so you get temsp under 40C load, then start increasign things to see what your max OC is. Then you kn wo if it is worth it getting better cooling.