US M030 is
not lower than the standard suspension. The springs are, however, an unknown amount stiffer. Hopefully I'll get my hands on a set soon and make some calculations based on the coil thickness. The shocks assuredly are valved differently as well, but who knows what the difference is.
The front US 030 springs are the same for all Boxster, S, Tip / 5-speed / 6-speed. There are three sets of factory Boxster springs. US Standard, US 030, and ROW 030. Simple. ROW 030 does lower the car slightly. Again, US 030 does not.
The rear US 030 springs are different depending on if you have a Boxster, Boxster S, Tiptronic or non-tiptronic.
They sway bars are as follows, and all the bars for US 030 are the same as ROW 030.
Front bar:
Standard suspension 2.5/2.7L Boxster: 23.1mm diameter, 3.4mm thick.
Standard Suspension 3.2L Boxster S: 23.5mm diameter, 3.5mm thick.
M030 2.5/2.7L Boxster: 23.5mm diameter, 3.5mm thick (same as standard 3.2L)
M030 3.2L Boxster S: 24.0mm diameter, 3.8mm thick
Rear bar:
Standard suspension 2.5/2.7L Boxster: 18.5mm diameter, 2.5mm thick.
Standard Suspension 3.2L Boxster S: 18.5mm diameter, 2.5mm thick.
M030 2.5/2.7L Boxster: 19.6mm diameter, 2.6mm thick
M030 3.2L Boxster S: 19.0mm diameter, 2.7mm thick (yes the 3.2L M030 rear bar is SOFTER than the 2.5L / 2.5L M030 rear bar - strange).
Hope this helps clear up (!) some of the confusion.
