Tench, Re: I don't know how you arrived at an upper limit of $4500 for a "good single-P4 computer."
Easy. You take a Pentium 4 computer with all the hardware features you can possibly think of, multiply it by a factor of 1.5 for the hell of it, and then you'll arrive at $4500.
Tenchu, I saw the $4500 P4 computer in the latest "computer shopper" magazine. It was one of the reviewed comps, the most expensive one. To be fair I should say that they also had an Athlon-based comp with price tag close to $4000. And they had a bunch of $3000 P4 systems as well.