Do you have Enable Harware Shading on in the preview settings? If yes, switch it off for this scene and see if things speed up. If you don't have it enabled, try switching it on, it may unleash the real power of your gpu.

I'm sure you've tried switching between the PBuffer and Scene Window, if not give that a try.

There also is the Preview texture resolution slider. With this being one huge prop, I would set it lower then usual, that could speed up things a lot.

For other scenes go back to your usual settings if they work fine for you, but for this one try some different preview settings.

Artwork and 3DToons items, create the perfect place for you toon and other figures!

http://www.renderosity.com/mod/bcs/index.php?vendor=23722

Due to the childish TOS changes, I'm not allowed to link to my other products outside of Rendo anymore :(

Food for thought.....
https://www.youtube.com/watch?v=pYZw0dfLmLk