Thanks for the responses. I guess I started off with some terminology problems in my original question. I now realize that all Memory Sticks are "Pro". Some are just "Pro" and some are "High Speed". So, as your answers stated, the question is really one of speed.
As an aside, is there any reason to consider getting a Pro Duo instead of just a Pro stick? I know that the Duo is smaller and will work in the PSP handheld gaming device. And the Duo must fit in an adapter to go into most Sony cameras. Any functionality differences between the Pro and Pro Duo? Thanks.