Lowered mine last week as well (inspired by Telford Mikes experiences!). A supposed 25mm on Spax spring, but on measuring is about 30mm. Its done wonders for the handling. Flat as a steamrollered pancake. However, as someone mentioned in a thread on the main forum, the car will slide easier in the wet, which, incidentally, is just about the first thing that happened after I got it back from the muppets who fitted the springs. Sharp left turn, lifted off a wee bit too much in the wet, and bye bye grip. Utterly amazing in the dry, but I must display a bit more caution when the roads are damp. Until I ditch the not so great ContiSports, that is. Go for it, a cheap and very worthwhile modification.
Rhys