I had an 08 M8, still have an 08 M1000 with speedwerx set up, and now have a new 2010 M8 153.
I can tell a huge difference between the 08 M1000 and my new 2010 M8... I can't comment on the weight difference between the 2010 m1000 and the 2010 m8 but All I know is that comparing the 08 m8 and 08 m1000 the m1000 was a tank, pulls like a tractor like everybody says...
putting the same 08 m1000 motor in the newer chassis, minus the lightweight crank... still a heave beast, and the new M8 has 160ish hp out of the box. whoever said "put a lightweight can on it and blah blah lower the weight difference to 5 lbs" .... you are going to do all that to an M8 too, which has the M1000 suitcase of a can on it by the way... so anyway you cut it, the M1000 is always going to be much heavier than the M8. I love my new M8 with the 153, but I would like to try the new M8 in a 162 because I think it could easily handle it no problem. My 153 '10 M8 is a wheelie monster stock!
Anyways, sounds to me like you should rock a 2010 M8 and you can go with either the 153 or the 162... i don't think you will tell a difference in handling but the 162 will truck you up a bit farther.... my .02.
Ryan