I've noticed pretty dramatic slowdowns happening in dungeons and only dungeons, everywhere else I generally see 50-60fps, my pc is an i7 at 4ghz with a Radeon 5970 and I've noticed this happens in vanilla Morrowind too so I'm pretty sure it's not mod related.

I've tried tweaking the lighting options with no luck, the slowdown appears arbitrarily, I could be staring at an unlit wall and get 15fps, noclip through the wall and there's no hidden geometry behind it, just an empty cell with a water plane, so it's not some badly optimised mesh hidden out of sight.

Any ideas?

*edit* problem found but not quite solved, MGE's distant lands apparently causes slow down in dungeons, there is an option to disable distant lands for interiors but it apparently screws up *all* distant lands, making them appear solid black.