Well, strictly speaking, Photoshop doesn't do renderings, at least not from 3D to 2D. However, if you have enough RAM to work with your images without having to page out to the hard disk, many operations will be faster, sometimes a lot faster if your hard disk is relatively slow. Processor speed will affect it, of course. Photoshop is a multi-threaded application, so it will take advantage of multiple processors. Not all applications will be affected by multiple processors unless they're designed to do so. Now having said that, you can configure Photoshop to use as much or as little of your RAM as you want it to. Gromit