As I am a geek, I did some dragy runs and virtual dynos with my 2008 135i when I purchased it.
Firstly with stock ECU Map it ran 13.4 1/4 mile.
With Stage 1 it ran 12.93 1/4 mile.
With Stage 1+ it ran 12.75 1/4 mile.
So this gives you an idea of the difference Stock to stage 1 and stage 1+ makes on these cars.
I didn't run stage 2 OTS tunes to test, as I went full send and upgraded turbos etc.
But to get an idea of some serious power, here is stock vs 17T turbos with inlets etc.
Quarter mile not tested officially, its too fast to test without a drag day, but its a lot faster than my 11 second 335i.