Memtest. But memtest is a sector by sector testing tool. But that tells you if you have bad memory. Not if it's not friendly with an overclock. When you are clocking DDR4 to 3000GHz. You are really clocking the memory bus to 1500MHz (Because DDR) you are not actually overclocking the memory chips themselves. There is a little more to it. When overclocking you aren't generally increasing the likelihood of increased bad sectors, but the strain on the memory subsystem.how much ram is used? why not test all the ram if talking about stable overclock for ram. i guess i can just keep asking over and over how do you test memory that is in use by operating system already...
So decide what you are doing
Bit tests. Memtest
Memory subsystem tests. One of a 100 different 24+ hour benchmark tools that do tons of memory calls.