Best way to test CPU and RAM stability?

[Caribou007]

Dual-Core CPU and two RAM sticks running in Dual-Channel mode. I underclocked my RAM and ran the Prime95 Small FFTs test with a single instance of Prime95 and 2 threads and determined the top stable speed with a 27+ hours run. I also tested the RAM for 12 hours with Memtest86 at it's specified configuration and with the CPU at it's stock configuration. Then I set up the CPU with the configuration I had determined was stable, and used the Memclock to CPU Limiter to avoid overclocking the RAM. The resulting, final RAM clock was about 1.5% below it's specified, (and tested), stable configuration.
However, my system freezes, every time. After about 1 hour.
I found that by increasing the voltage to my CPU, or by decreasing the CPU overclock, I could avoid the freezing, or at least it seems that way. So it seems that the Prime95 Small FFTs test was not sufficient to determine the CPU overclock. Perhaps I need to be testing the memory controller as well. Perhaps the memory controller requires additional voltage, and that explains the problem.
So what's the best way to determine the actual maximum stable overclock? Should I run two instances of Prime95 with their respective affinities set to each CPU core, and have one do a single threaded Blend test while the other does a single threaded Small FFTs test? Two single threaded Blend tests? What is best?

 

[Woomack]

Prime95 blend test should test both cpu and memory good enough to be sure that everything is fine.
You can also try something like AIDA64 where are cpu and memory stress tests.

 

[Caribou007]

So for my dual-core CPU, run 1 instance of Prime95, Blend test with 2 threads, for 24 hours?

 

[Woomack]

You don't need 24h, usually 5-6 will be more than enough.