Be certain that you run Small FFT's, but NOT Blend. Small FFT's is the standard for thermal testing, since it's a steady-state 100% workload, which allows consistent and repeatable temperatures at a given ambient.
Since 97% thermal saturation is typically reached within 7 to 8 minutes, a 10 minute test is adequate. Small FFT's test durations of more than 10 minutes will yield less than a 1c increase.
Blend is a cyclic workload suitable for memory testing, and causes fluctuating temperatures, which is inappropriate for processor thermal testing.
For more detailed information concerning temperatures, click on the link in my signature.