Why PPK? Is your car under warranty or an N55?
Id go for COBB - been superb on my N54 car. PPK gains are very minimal but you do get to keep the warranty.
Current: 2011 F20 120d SE
F21 M135i on order!
E90 335i, 2010 Alpine White N55 135i 6MT, 2009 LMB LCI N54 135i - Cobb tuned!, 2010 F10 530d SE, 1986 E30 318i,1981 E21 320i Auto