What are your temps in Prime95? The CPU will run up to 100C then shut down. I wouldn't want to run about 80C even under Prime95. If your running way about 80C in Prime95, check the seating of each of the four push pins on the stock heat sink. And look for any light showing between the CPU & CPU cooler base.
I have an i7-860 and found the stock cooler just wouldn't cut it. If you need to lower temps till you save up some cash for an aftermarket cooler, go into the BIOS and disable HyperThreading. This will limit the system to running on 4 cores and not it's full 4 cores + 4 threads. Temps will be much lower. About 10--15C if I recall.