+1
Mine are about 15mm lowered - when Abbey did it they said that they could drop it 15mm using the same camber arms, dropping it more than that (and they said they could drop her 30mm without any problems) you need different camber arms to set the wheel camber correct, but essentially you can drop it as much or as little as you want.
Just in passing - even dropping her only 15mm I run into bottoming issues as the UK roads are so poor. (and in NI and Scotland even more so!) So - if you're going to lower her much, it'll be great on track but be warned! Speed bumps get to be a real pain in the A$$ - literally as well as figuratively