let's see cross fire will take the offtrail hands down, sx probably takes the tight and twisties if set up correctly w/the right rider, and the dragon will be first to the bottom of the lake.
on an honest note you'll like the 900, it was my first sled away from yammi's and i do like it. they take the bumps pretty well, with minimal tinkering they run well, only thing i will complain about is the diamond drive's weak and I can't get the suspension dialed to keep the front down enough to rip through the turns like on my old sxr or srx(couldn't get the rx to either due to ride height)
as far as mod's go you're going to get many different ideals. I ended up going d&d twins(i'm so so on quality), timing key, vforce, clutching(you've got to match your power curve), cut heads and porting and am now happy with the power with it. best bang for your buck would probably be the timing key, pipes of your choosing depending on YOUR riding habits, and clutching