LinX and Prime95.
I know a lot of people will complain that Prime95 version 27 and up producing too much heat on Haswell processors and that it is not a real life scenario, but for me it is. Prime95 loads the floating point units on the CPU producing more heat than normal, but that is perfectly in line with what I get when rendering with Mental Ray/Vray on Haswell system.
Depending on what you do, your system might be stable or not. If i just game, I can run 4.2 GHz at 1.17 vCore. If I render, I need at least 1.19 vCore. AIDA is stable at 1.17 for me. Prime and LinX are not stable and crash at that voltage.
If you are doing more than gaming and you want to ensure that your OC is stable - the best pounding you can give your CPU is...