never heard of FO3 messing up an xbox
Neither have I, and I certainly didn't mean to imply that. I was just trying to point out that they are two games build on the same platform with the same game engine, and they've had equal problems with lag-- which for the most part, outside of the stuttering problems with gamebryo, aren't bugs but just limitations of the xbox itself. The only game I can think of in recent memory at least that actually killed things was starcraft 2, because there was no frame rate cap. But to people like the person who responded to you saying they got the RROD from FO3, that has 99.9% to do with the crappy design of the xbox itself: air flow svcks, it's got a dinky heat sink. A monkey could have put together a more durable game system. A lot of that drag and slow down is because you're having to render so much, it's a side effect of having an open game world with so much detail, and something that's a hardware/processing problem, not so much a game problem. GRANTED, that can cause GPU to start heating up, but it's the shoddy construction of the xbox, with cheap soddering along with the problems I mentioned above with inadaquate heat sink and air flow, that kills the thing.
Now the clipping, falling through the walls into a white nothing (that's happened to me once, in the visitor center at hover dam), those are certainly real issues worth complaining about. But people complaining about a lot of the slow down and lag, if it bothers you that much then don't play on xbox. That's about the only solution you're going to get, because you can solve some of that with updates and fixes, but for the most part it's like trying to play a brand new game on a five year old computer: it's not going to work so great.