Bruce, since you brought up perceived RS4 vs. M3 torque differences at the low-end several times, I couldn't resist thinking about the numbers. Here they are for both cars in 2nd gear. Obviosly, the RS4 will have more traction below 2500, but how much more and is that enought to offset the weight difference? (I assume we can agree that rotational intertia issues are pretty much a wash here.)
On the part throttle issue: what throttle mapping did you drive the M3 at?
Values adjusted for temp and hum.
http://www.rri.se/index.php?DN=29