I had *no* stability issues when I had my XP1700+ under a Arctic Cooling Super Silent Pro within a really small case (PSU mounted right over the CPU Cooler) and the one time I checked the temperatures I got:
Idle, case OPEN: 58°C
full load, case open: 68°C
full load for 6hours, case clased: 76°C
I never had any stability issues, nor has the CPU failed (yet
) or something.
Now I have an SLK 800 with a 8412N/2GLM Papst fan within a standard ATX tower, temps are around 49°/51° and I'll definitely do something like upgrade my CPU or get a slower fan, cause to me any temp around 60° feels perfectly good which means I have some resources left.