I wouldn't bet the family jewels on it, but I do believe the 60/40 torque split was newly introduced on the B7 S4 (and only on the manual transmission cars).

As for which is the preferred year for B6s, my guess (and it's completely based on just common sense - which isn't saying a whole lot, haha) would be the final year as that'd be when the year-on-year improvements and refinements have culminated in the "best" B6 possible?

Not sure if that was much help.