Actually, ATI now refers to EVERY combination of their cards as "CrossfireX".
I believe what enaberif is talking about is using a system with MORE than two cards (which used to be called CrossfireX). If this is the case then he is correct that more than two cards will not work in XP.
Fair enough, So why is my cross fire so slow? I tested it in vista 64. Looking at your benches I am faster than your 4850 results with one card yet slower than yours with 2. I get 15300 with a single card and 17300 in crossfire.
I think many have been down this road before.
Hanging around tech forums such as this one sometimes has the effect of losing touch with reality. The perception of a perceived gain in performance when dishing out your hard earned cash is hard to digest at times when you experience the results.
The cash spent on hardware to increase performance rarely justifies the amount you spent