some pics comparing:
1) Legacy GT strut (no spring, showing yellow bumper),
2) Bilstein Legacy GT HD strut (with spec B tophat...which adds a little height compared to stock OB tophat: YES it does!!!))
3) OBXT strut / spring
and on the other picture
4) the silver JDM Bilsteins I found with stock OBXT spring cut by 1/3 coil. these use normal USDM tophat, not the spec B tophat)
All bottom mount holes are lined up, so any variation at top of units shows dimensional differences.
note, legacy shortest, then HD, then stock OB (actually an 05-09 KYB aftermarket), then longest is the silver JDM Bilstein.
each little square on my floor is 1/2 inch.
Mount them on the car, loaded down, things obviously change: the JDM's are the tallest, then OB, then HD (shortest). I THINK the JDM's are tallest, not because of the strut body length, but because of the gas pressure (in conjunction with the fact that the strut CAN extend further), and the HD's have lower perch and shorter travel, but gain back a bit because of the Spec B tophats. I never mounted Legacy struts, but assume the shortest of the bunch mounted, in actual use. I would have thought that JDM's would have equalled stock OB, since lower body is identical SIZE (although smaller perch...no "basket"), but they extend further and weight of car doesn't comepletely negate Bilstein gas pressure.