Doug,

Based on our extensive testing of dual core vs. quad cores you don't really get the advantage of quad cores unless you're running true multi-threaded applications. None of the ones I saw on your list are really going to take advantage of the extra processors. Most of the time the extra processors are just sitting idle. We have noted that multiple CPU graphics cards actually give more bang for the buck.

Having tested HP's and Dell's side by side I've come to the opinion that I'd rather have an HP. They seem better built, their on-site service is better and they last longer and generally perform better.

For a limited set of test results you can go here,