You could run prime as suggested and wait for it to fail, normally overclocks which are as stable as a 1 legged table will fail prime within minuites.
If we are talking A64 here, I put the memory on a divider and keep it around 200mhz, even if the divider means running the ram at less than 200mhz, then do so.
Then start upping the HTT in about steps of 20 or so, you will find the point of major instability quicker that way, once the rig either doesn't post or fails prime you know thats when and you can either back off and find the most stable clock for that voltage, or up the volts abit at a time so you find the minimum amount of volts for that clock as possible.
Once your clock has been found then start trying different dividers for your memory to see if you can up the badwidth, even though bandwidth isn't important in real world performance a lot of people still increase the speed of their ram when talking about the A64 platform.
You could also try programs like OCCT which complete within about 36mins or so.
