208871 Oscommerce Speed Optimization

I am looking for a programmer to help optimize an Oscommerce web shop. The shop is very slow now. The shop was customized and has over 6000 products. It seems the more items are added, the slower the pages load. I would need a short analyze of the web site, to know what the problem is. The amount of database queries must be reduced, and a caching feature implemented. The basic goal is to considerably speed up the site. I would need a short documentation, what was changed. Must have experience with Oscommerce.