I had a 2003 XT 225 and felt exactly the same as you do. The XT was fun off road, but it was sorely lacking hp and torque for the road. I researched the 2008 FZ6 and finally bought a new one in August of 2008. I've put 2,300 miles on my FZ6 since August and have loved every minute of it. The FZ has WAY more power when compared to the XT bike. It's road manners are far better as well.
I can't comment much on the R6S because I simply don't have much experience with them. The FZ6 and R6S share the same exact engine, so hp and torque will be close. The FZ makes it's power lower in the rev range while the R6S makes power at higher rev's The FZ6 will have more of an upright riding style while the R6S will be more "rider forward" similar to a full-on sportbike.
Each bike has it's merits, but for me, the FZ6 won out. The FZ is more comfortable for my long legs, and I don't have to lean over the tank.
Happy shopping!:thumbup: