What are your specs? Keep in mind when running a high LOD with super resolution textures you are forcing your video card to load much more data than would be normal, so you will need lots of video memory headroom. That texture set is nearly 1GB, so even if you are only loading 1/4 of the scenery in the highest LOD that's 250MB of data. Are you using supersample AA? That takes a lot of texture memory, so try going to 4x multisampling, and if using 4096 clouds drop those to 1024 and see what happens.
@ Bob, great shot!