My 335ix is by far the smoothest turbo I have owned. My previous Turbo's (911,and Starion) came on like a light switch and were quite non linear and could be scary
. A friends 911 Turbo blasted on when he downshifted on a interstate exit ramp, spun into the curb - 18K in damage to the mechanicals - the half shaft pushed into the trans. I have a X3 3.5 in production this week, and although I suspect it will not be as quick as the 335, it should be quite linear in power above 1500 rpm as the torque is constant.