Have seen some great shots and user comments on the new 150 D, but for folks that have used it, how does the older, M645 150/2.8 A rate?

I have the 150/3.5 (plus 80/1.9 and 200 APO and testing a borrowed 55/2.8 on a 1Ds2) and quite like it -- and was curious of the IQ of the 2.8. Have yet to be disappointed by any of my M645 glass, but there will be a first time..