Hi,
I had the same several weeks ago and called Appian. I spoke with a technician about intended use (ie. trading, not high-end graphics), and he stated emphatically that the Rushmore was what I wanted.
The Rushmore is Appian's newest technology card and it has only been on the market for 2-3 months.
The Appian website stinks, and I told them it was very difficult to distinguish the difference between these two products. Perhaps the rumor that the X is being discontinued hints at why.
I decided to buy a Matrox G200 MMS Quad now for the following reasons:
1) the Appian software for working with multiple monitors, which is acknowledged by many to be the best, is not ready for XP, and they could give me no solid information as to when it would be,
2) the G200 is found for good prices right now as there are new products coming out at Matrox to replace it. However, Matrox made it clear that the Matrox would continue to be sold until probably the 4th qtr, and hence well supported,
3) you can buy a new or used G200 MMS on eBay for pretty good prices... a used one went for $240 just a couple of days ago...I paid $285 for a new one, but watched eBay for a week or so to get it
4) you can run it side-by-side with a Matrox G550 to get six monitors...the G550 can be had for close to $100 if you look.
Finally, installation of the Matrox card on my machine went very well (once I figured out how to turn of the onboard graphics in my Compaq).
I will in the future consider the Appian cards, but they seem a little behind the ball at the moment