i've found it's much better to have the amp running at a considerable %age of its max output..i'm not talking about gain here, but actual master volume.
i think it's better to track with a small amp running at 75% than a big amp running at 10%. it just..sounds better!
i heard that for a lot of Led Zep Page used small practice amps in the studio, rather than his live rig. i think it's just a question of actually getting the amp to run hard.
EDIT: if you want that real big, heavy, "wall of guitars" sound, than do just that. track loads and loads of guitar parts all on top of each other, this isn't really an effect you can fake. i was reading the article in Sound on Sound about the new Darkness album and the produce said that in some songs there were as many as 120 different guitars playing simultaneously..i'm not suggesting you do that (nor that the Darkness is what you're aiming for) but it's just an example of how people achieve that "heavy" sound. make sure that when you're listening to the amp, it's got that heavy sound to it..from there on capturing the sound is a question of layers/mic placement.