Typically if there is an error your computer will flat out class, often with a BSOD and BSOD codes. The codes for Haswell bsods are 101, 124, and 9c.
Other options for stress include OCCT, XTU, x264, and even chess.
If your Vcore is higher, your VCCIN aka Vrin aka input voltage should be raised as well. For example, at 1.35v vcore, 1.95 VCCIN was more than enough. One multiplier up, I needed 1.42v and 2.15v VCCIN. That was my voltage wall and I found that raising that Vcore from 1.35 to even over 1.5v, which, crazy Darkwizzie did, did not cause stability.
As a last resort once you can't figure out what's happening, you've exhausted this guide and my guide, then what you can do is run a stress test multiple times on a given setting, then change one variable and see if there is a change in average time till' Bsod. This is very time consuming however. It did help me discover that for me at such high Vcore, the VCCIN I needed jumped up a lot, and that was how I found my stable settings.