Memtest only tests the memory, you will want to use Prime95 or some stress test to make sure the entire system is stable, along with the memory.
Glad to hear it worked.
If you want to be "overclocker" precise, test for the lowest stable DRAM Voltage and QPI Voltage. The QPI Voltage especially can vary on AUTO, so manually setting this would be best.
Thank you
GSKILL TECH