I very definitely noticed the difference in power with my stage 2 PPK upgrade. Also, it adds a nice mix of pops and burbles to the exhaust during engine overruns, and the exhaust note is deeper and more aggressive when the gas pedal is dropped.
When playing around with the iPhone app PocketDyno+, I managed a 0-60 in 4.8 seconds. That was without brake-revving and with a bit of wheelspin off the line on my crappy 17" rfts... and I weigh 250lbs. Tank was 3/4 full too.
I think if I did some serious runs, I could drop down to 4.6, maybe.
2011 E90 / Premium Package / Stage 2 PPK / Performance Suspension