Let me know if this helps:
I had a stock 2007 335i. Now have a 2010 335xdrive M Sport with PPK and performance exhaust. Huge difference in performance IMO. Don't know the exact numbers but BMW ALWAYS underestimates HP and there is no reason they didn't underestimate the added HP with PPK and performance exhaust (which is supposed to add 5HP by itself). If I had to guess I would say the combo of the 2 packages added 35-40HP.
I just ordered a 2013 335Xi MSport with PPK (option Z3B) and Performance exhaust (option Z10). PPK price: MSRP $1370 (wholesale $930). Performance exhaust price: MSRP $1335 (wholesale $885).
To me the package is worth the extra $$ for the following reasons: I wanted the new M3 but cannot wait as my current lease is coming to an end. M5 a little pricey for me. As I am leasing, I get the extra kick and keep the warranty. I am only doing a 2 year lease on this one so I can get into the new M3.
Also, the new PPK and exhaust is just beginning production and none have made it to states yet, probably not until early December.
As far as the exhaust sound, I do not expect it to differ much from the performance exhaust kit I have now. It is a little loud for my tastes but just for the fact my wife dislikes it, makes it worthwhile. Keeps her from driving my car. No drone and sounds awesome at full throttle off the line. People notice.
2013 F30 M Sport/xDrive/Black Sapphire/Black Dakota/Performance Power/M Sport Exhaust/AT/Premium/Cold Weather/Tech/19"