This tip was presented recenty: turn everything that is covered with clothing invisible, not there, no need to render. I would check all the shadows and reduce as much as possible while maintaining the effect. Check trans maps, they can be a killer. Get rid of all the temp files in windows>temp folder. De-frag hard drive. If all the above doesn't help, go out for a cup of coffee.

I must remember to remember what it was I had to remember.