I had a CF7SP with a 144 so basically an M7. I went to an 07 XRS. Differences...It took me quite a while to get the hang of the REV but now feel really comfortable on it. Like posted previously, everyone is different. My bro has an 09 M8 which is a really strong runner but the motor on my XRS is certainly stronger on the bottom end, but top end, or hillclimbing they are pretty darn close. I would not hesitate for the REV as most say it's one of the best mountain chassis ever made. As far as the 07's go, as long as the motor has been updated, you should be good to go. Now the early replacement motors with the correct crank tolerances did have the "R" stamped on the case. However, guys in my riding group on the xps do not have the "R" stamped on the case so as long as it isn't the first replacement motor, you should be good to go. I have over 1500 miles on mine and crank tolerances are still great and there is no "R" stamped on my case. Good luck in your decision!