It's very possible you run p95 for 50 hours only to crash in 5 minutes on h264 on a slower preset, but it's not likely. You need to make sure WHEA errors aren't occuring during your p95 runs.
If I set LLC so there's still a little vdroop, the CPU will run on lower voltage while prime95 is putting load on it. I'll test with prime95, and then I can assume that normal programs will run with the CPU getting more voltage.
If I use the max LLC setting on my board, voltage will actually increase when prime95 is doing its stuff. Normal programs will run at a lower voltage than what the prime95 stress test ran at. Could this be the cause of prime95 running stable but programs still crashing afterwards?
Doesn't quite work like that. Your software won't tell you your accurate voltage, it just tells you an average, so your peaks and dips aren't going to be truly reported. It's very likely when your voltage starts to go up, that it'll report decreasing voltage. You have to use a multimeter to get accurate voltage read-outs, even with high end boards...
What LLC does is make it so your voltage 'dips' less, as your voltage is essentially a wave, up and down, up and down, very quickly. It's never stable at a set voltage, software just reports an average to you that's easier to read. However these dips let your CPU use less voltage, it keeps the chip cooler and use less voltage when it doesn't need as much. Raising LLC means your chip gets much hotter as the dips are smaller, and your true voltage has much less variance, but your peak voltage gets much higher.
When overclocking you pretty much just want to use the 2nd highest LLC setting. The higher you set LLC, the higher your voltage, but it also increases temps. So generally, on ambient overclocks, use max LLC and you'll need significantly less voltage for stability, but your true voltage will be much higher as Vcore = VID + Offset + LLC. But on too little LLC, and you generally need to raise your voltage so high that it'd be higher, than if you used just the 2nd highest LLC.
Vdroop is a good thing, it keeps your chip much cooler. You can get an approximation of your voltage using software, but you can't determine things like vdroop, by the very nature of how your system reports an average, things like vdroop aren't reported. Of course you are going to be more stable on max LLC, that's because you are adding more voltage. The idea is using the ideal LLC setting, you need less true
voltage than you'd need if you didn't use it or used the wrong LLC setting.
Unless you want to spend tons of time testing with a multimeter, like myself, sin0822, and a few others have, just set your LLC to the 2nd highest setting when on ambient overclocks. Many, many people have proven that the 2nd highest setting is the best for air/water.