What map have you got? It makes a difference ... BMW produces all sorts of variations of the stock map to refine it over the years. Also some people poo poo the
JCW map as a pile of cack compared to the stock map. I run a stock map that was last updated in late 2006 and it has a wonderfully smooth power curve on the stock car, recently it also showed a nice smooth power and torque curve.
RMW in US dio see some major improvements on many of the cars they tune in the states, as do 1320 via them in the UK. However if you have a good map, and mine appears to work well.... its perfectly viable to use a stock one and tweek parts to make it work better on a tuned car.
Also you may not have a map problem, you could have a retardation probklem, timing, boost sensor problem... all sorts of things that can make the car feel like its not delivering its potencial... i may not be the map thats the issue, but a small inoccuous part that causing the car to hesitate or hold something back ... The tell tale is your feel of supercharger lag. Superchargers shouldn't lag really, not in the typical sense like with turbos. What revs do you require before the 'lag' goes and she starts to really fly?
