Well, it's a graphics portfolio, people going there should expect it to be picture heavy. If loading pictures is going to slow them down too much then they should know better than to go to a site that they know will be loading 9000+ pictures.Background is personal prefrence....
The site is good, your using wordpress which i wouldnt advise...
Also with each members portfolios a link should lead to the photo, rather than all photos on one page, it slows down the PC and uses unnecessary browser power. But apart from that its looking good! I like it