I found a thing, which of course I won't be able to find again now.
I'm replaying through FO3 at the moment and I get constant crashing, well, just the game freezing, alt/tab out and loading up again, nothing system killing crash wise.
I found something saying limit the game to 2 threads, and what I assume turned on multithreaded AI.
bUseThreadedAI=1
iNumHWThreads=2
It was those two options in the .ini file. The first one is usually 0, the second line you add in after it yourself.
Before that I could easily have 10 crashes in a bad hour, or occasionally can go a couple hours without a crash. Since then I've played about 10 hours with one crash.
Of all the various "fixes" i've seen for FO3 over the years, its the first one thats made a difference.
New Vegas has the same options and is basically the same game so is worth a shot.
So many people have crashing issues with both games though, its laughably unstable with no out and out fix, no patch to fix things and really no idea whats causing so many crashes for so many people.
IF it wasn't a very quick loading game I'd have given up a LONG time ago.