Haven't dynoed my car so I can't report on that, but I do have the PPK. I had the same concerns as you about voiding my warranty, so I got the PPK. It was a bit better than stock, but nothing to write home about. Right now I've grown so used to it and want more power, alot more. I'm presently waiting to see what Cobb eventually comes out with for the N55, vs going with a JB4, in the future.
I'd say skip the PPK and get a JB4...if you are worried about warranty, you will already be inviting dealer scrutiny if you install a DP and FMIC. Plus, the JB can be easily removed before service appts and the like.
If you decide to go the route of DP, FIMC & Meth with the PPK, I will be really interested to see how much power you pull.
2011 E92 M-Sport 6 Spd Manual BSM/Black Dakota/Dark Burl
Heated Seats / H&K / Sat / Ipod/USB / CA / AST 4100s / M3 Suspension Bits / 18" Forgestar F14 - Gunmetal with Michigan Super Sports / Quaife LSD, etc...etc...