That method of testing works also.... i did a little different though. I had the SetCPU app before i got the jrummy oc app. I started with stock voltages and slowly increased to 1.25, 1.3, and so on (my phone runs up to 1.4 ghz ULV and the setCPU app ends at 1.2 and you cant change voltages). So each time i increased i ran the stress test in SetCPU for about 10 min then increased again and kept doing this until my phone froze and then went back to the one before. When it froze on 1.45 ghz at stock voltages then started over on low voltage. Kept doing this through low voltages and ultra low. I'd reccomend doing it this way because not every phone can run low/ultra low voltages.
You can get SetCPU for free off the xda forums by the way. (And no its not where someone payed and posted. The dev posted it on there with a donation link in it).
Sent from my Fissioned D2G