you want to run each one separately, not together.
superpi stresses your cpu to 100% as well as prime95... depending on which has priority, superpi or prime will drop close to 0% or maybe even 50/50 of the load...
best bet is...
cpu overclock = prime small fft's for at least 6 hours (some do 24).
ram overclock = memtest looping test #5 for a long time (this is dependent on you as people have reported different things about how long you should run this for).