Please see the most recent updates in the "Where did the .com name go?" thread. Posts number 16 and 17.
I think it was a Holger Sandmann tip (can't swear to it though), that said to use 3-D cloud percentage at 100% and Detailed clouds, as the other selections brought in even more frame killing 2D models. The Cloud coverage density is set at whatever your computer graphics can bear.
Here's my setup: