3-Stage intake installed today (new manifold, installed by dealer). Got a discount though and hey, a two year warranty too! (3.5 hrs labour to install.) Drove on the highway for 20 minutes under varying conditions: Cruising at 2000 RPM, 3500 RPM, Full throttle accel to red line in 2, 3 & 4th gears a few times, then some neighbourhood driving (hills). And....., well almost nothing to report. I think that I've lost some of the growl from my PI, and maybe the above 4000 RPM acceleration is better - difficult to judge as the PI noise was less but the speed gain in 4th seemed faster. No difference in low end torque or throttle response - both have always been pretty good.
Will edit post with any changes that come along.
'09 128i 6Sp Man Sport (263 18" wheels), Space Grey / Coral Red leather, BMW Perf Intake, Exhaust & Suspension, 3-Stage Manifold, AA Ver 2 tune, Carbon Filter & CDV Delete, Yoko S-Drives