Small FFT tests CPU Stability.
Blend tests overall.
Here's what I use.
8 hours of Small FFT, if it passes run 12 hours of Blend without restarting.
If it passes 8 hours of Small FFT I consider the CPU Stable, if it passes 12 hours of Blend I consider the mobo/RAM stable.
Then I leave it on 24/7 and see if I can make it crash.