Howdy! I own a pair of 2002 single X's in 184, and I love 'em. I tried out the XX's, and while a great ski, they weren't as quick edge to edge, nor were they as nice in the bumps. We received a lot of snow in January, February, and March 2002, and they were fine in powder and crud. I imagine that the XX might have a tad more float, but in general day to day usage I thought the X was great. If I could change one thing I would've went with the 177cm for even more quickness. I really like the sensitivity of the X, and the ability to really *feel* the snow in uneven conditions.
It really boils down to a personal thing though. Take both for a drive if you can, and choose the one you like best. The X isn't worthless though. Give it a shot. You might be surprised at what a really fun ski it is. Forgiving too.