I saw a post where some guy said he and his university comp-sci department did a bunch of testing, and determined that there were a bunch of memory leaks (some VERY big) and pointed about 5 separate issues about the game.
Some other guy posted saying that after doing some mucking around with the inis, he found that multithreading was the culprit of a good portion of his crashes. I even changed my ini, hoping that that was the case. No change.
Yeah, memory leaks typically happen after an extended period of time and aren't particularly easy to reproduce in most cases. Your issue is most likely a bug in the game. Given that it's Bethesda that we're talking about, I wouldn't hold your breath waiting for a patch. Oblivion is still horribly fucked up and that game came out in 2006.
Speaking of Oblivion, I think it's really fucked up how poorly the game runs on high performance machines. Several people I know, including myself, have attempted to play Oblivion on hardware that absolutely
destroys the top of the line gear that was available when Oblivion first came out and it still runs poorly. It's just like how Morrowind runs poorly on systems greatly exceeding its recommended requirements.
Sadly, I think Fallout 3 is Bethesda's best engine work, and it's
still piss poor. It really says a lot when my computer can handle Fallout 3 (and even the likes of Crysis, Far Cry 2, and FEAR 2) far better than it can handle Oblivion. They need to just give up and license id Tech, Unreal Engine, or something like that, because they couldn't program a fast, reliable engine to save their lives.