I did a fair bit of reading on the topic a while back... came across a thread somewhere where some dude did testing stock vs. drilled out rotors. Cant remember if it was m90 rotors though.. but the principal would be the same I guess... anyway, the drilled lighter rotors showed less flex and vibration.
Also, of the people I know here who are using the MACE Engineering lightweight rotor pack none of them have had any problems. One guy is using a 2.4" pulley and overdriven balancer and even the coating on his rotors is still flawless after a year or so... he's making 450rwhp with the m90 lol
As for myself, ive been using the light weight rotors for a month now.. and no problems as of yet.. and i'm not expecting any dramas at all.
