hmm, I didn't notice much trouble with 2048x2048 lightmaps in FMC and the leadfoot racer even on a 32mb Geforce2GTS on a 256mb Pentium 2 400. However if your using a lot of large maps your probably going to suffer. I generaly use 256x256 most of the time. 512x512 for characters and things that require a LOT of detail or take up a lot of screen space. And the really large ones for lightmaps, that get shared with many different objects.
Of course without seeing your game and how your using your textures its hard to say whats causing the slowdown.
Of course without seeing your game and how your using your textures its hard to say whats causing the slowdown.