6WD Chassis Stiffness vs. Maneuverability

[IKE]

For the last 3 years KB33 has been build 6WD aluminum sheet metal chassis. It has been an iterative design mostly focusing on more robust drivetrain. One thing we think we have noticed is that some machines seem to be more maneuverable than ours. In 2006 we were underpowered and had a difficult time executing turns. In 2007, we did a good job of holding our own, but there were faster and more agile robots. For 2008, we ended up going with an asymmetric chassis set up with 3 omni-wheels on three corners to improve turning. This was OK for Overdrive where D was mostly played on the ball, but would have been death in 2007.
So here is the question for 6WD teams:
Have any of you noticed chassis stiffness (most likely torsional) making a big difference in agility? I know that rock (amount of lift or drop on 1 set of wheels) plays a huge part, but with similar rock, we just don't seem as maneuverable as 1114, 254, and several others....... Could some of the iterative 6WD teams please chime in on this. If it is trade secrets, I understand, but if you care to share your knowledge I have open ears. I did a lot of analysis on slip and traction curves vs. speed and power consumption. My calculations model our chassis very well, but I was amazed to see that certain teams seem to defy the physics I know. Is it an illusion and you guys struggle with scrub balance, or do you just have a better tuned chassis?

P.S. Let's please stick with 6WD design discussion. I realize there are a lot of pros and cons to other designs (swerve, halonomic....), but would like to keep this 6WD related.