Well, 21 hours and 18 passes later Memtest still reports no errors. I hate to actually replace my RAM without knowing for sure there's a problem with it.
As an experiment, I uninstalled Ad-Aware altogether, just to see if that has an effect. Like I mentioned before, the only change to my system prior to these crashes happening was that I updated Ad-Aware. I don't know if that would really cause the problem, but I have Malwarebytes anyway and Ad-Aware was taking a long time to load at startup anyway.
I'll report back if that happens to have an effect.
Otherwise, any other suggestions? Anything in particular to be done about the "Page fault in non-paged area" error that maybe involves just uninstalling something or running other tests?