I had the CPU replaced on my '04 GT
The symptoms on my bike were exactly those which I recall as first getting my attention over at the dearly departed I-BMW.com
Namely, although the bike would always start right up the motor would bog/die upon any quick throttle application until warmed up a bit.
Slow, deliberate throttle application could be achieved, but a quick twist would not fly.
Additionally, once warmed the idle would occasionally fluctuate for no apparent reason by as much as a few hundred RPM.
The CPU replacement totally remedied those two conditions on my bike.
I can't say that I notice any other improvement in performance with the exception of fuel mileage.
I'm fairly obsessive about tracking my MPG on anything I own. Before CPU swap I was 'round 41ish, after swap 43ish.