Musky - I came from an 02XC8 with M-10 as well.
Vibes on the Fusion are about the same as the XC. You probably just didn't realize after getting use to the smoothness of our RX-1's.
My bud got a Fusion and I put about 15 miles on it. I liked the fact that with the handlbars back - It felt just like my XC.
For the first 200 miles he got around 6-7 MPG then after that (we put on 800 miles together in 3 days) he was getting almost 11. My 05 RX-1 gets about 12 1/2 - dissapointing compared to what everyone else seems to get with the RX-1's but still better than the 10 we got with the XC8's.
I'd say the M-10 and Monoshock are pretty even skids - give a slight edge to the Monoshock because of a little better transfer - it seems to resist bottoming better when setup for hard riding and mogul mashing than my M-10.
I don't think the RX-1 will be able to handle as well as the XC-8 on the tighter trails without adding some aftermarket mods - but I hate to spend the money knowing that it still probably won't be better from everything that I read. Not bad handling - but that extra 70 lbs carrying into the corner and the fact that on the gas out of the corner always pulls the skis off the ground (have slightly more ski pressure from transfer settings than I normally would too, so I don;t want to adjust that anymore).
Overall - I'd take the RX1 still - but I have a hard time shaking the comfort level of the ergos with the XC chassis.