Okay, so with the new cooler AND the new CPU, I'm currently sitting at a stable (so far after four hours of non-stop stress testing) 5.0Ghz at 1.38V. I'm going to likely reduce it to 4.9 at 1.32v and keep it there, since the temps were around the 80s, and they're currently in the mid 90s at 5.0, but it looks like I was right. A combination of a crappy CPU and a sub-par CPU cooler.
I did try running the previous CPU with these settings and it just nope'd out almost immediately. So I think I'm quite happy with things as they are. And now I can sleep now that I have a working computer again. Oh, wait. No, I can't. I'm behind five videos. x.x