My friend was constantly able to "put the power down" sooner during corner exits than my TI with 235 tires compared to my 255s. He was also much quicker in transitions than I was. You would suspect that he may be a better driver but we actually switched cars for a few run at an autocross and the time in his car as always quicker.
Note that we had very similar mods but my car has about a 400 lbs weight advantage.
http://www.amazon.com/BMW-Enthusiast.../dp/0837602203 This book actually goes into detail about the why the TI got the different rear-end.
I actually did alot of research on this during my 318ti LS1 project consideration.
I'll try to scan it tonight Jess so we can discuss further.