my previous 16s had a tyre of 165/40 (stupidly small) and was lowered about 120mm (helpers still in) withthe small height of the tyres it worked out i was about 140mm dropped and 20mm off the floor. would catch everywhere.
slightly bigger tyres now, 185.50 (which i will be swapping as they rub the arches)
195.45/40 on a 16 and you could lower it 100mm fine..
oh and mine didnt have any arch work i just ran loads of camber.