How were the files encoded? And what playmode were you using? If you were just using the play loop forward mode, then you might have had a significant number of files playing back at the same time. If this was the case, then changing to play fwd if > then 0 will help. Hard drive speed is the most important thing here, and more ram wont help you very much (if at all). Unless you want a few specific files only to be played, in which case you can add more RAM, and create a RAM disk to play the files off of.

There are always a number of factors that can affect playing back multiple files. Also, with high-motion files, the codec and quality become much more important. Did you view the files outside of catalyst on the same computer and see how they played back?