Have you tried
Core Temp? It's pretty accurate.
I use it or
Real Temp when torture testing, and I haven't seen much of a difference between the 2.
EDIT: For the ultimate torture test, use
IntelBurnTest. Set the number of threads to 8, the memory usage to max and it will get your CPU hotter than anything in real-world usage can. IntelBurnTest uses LinPack, which is what Intel uses to stress test their CPUs before shipping them. Use it in conjunction with either Core Temp or Real Temp, run it for an hour, and, if its max temp is anything below 85C (it can actually be anything below 90C; 100C is the supposed max, but 85C is where I draw the line), you're fine.