OU:

OCCT/CPU for CPU
OCCT/MEM for northbridge/mem timings
MEMTEST for Windows (!) for memory test

A OCCT test alone (maybe only on CPU) wouldnt find a lot.

Besides i assume you use latest OCCT 2.0.0a/b....then at least one hour at "mix".

Add: forget *bootable* DOS memtest. Its really only good for checking whether ram is defective.