@ FriendlyFire, try shrinking the size of your cloud and light textures, FL will still map them properly it's just that they'll be lower in detail. High detailed textures might look great in renders but in a gaming environment their next to useless, especially in MP.
I use Argh's pretty planet model as well but I don't use the same sized textures as he did, 1024x1024 for something like Earth & 512x512 for anything else, I use 256x256 for clouds/atmosphere. Yes my planets are low detail but FL is a low detail game and my planets don't look out of place in it, and I don't have the headache of dealing with massive mat files *shudder*.
**shuffles of with a new headache**