mate, tbh you have 2 dilemas..
firstly, the lower you go the worst the handling will be, 20mm is fine for everyday driving, you may still be able to go in multi storeys etc, 25-30mm is still ok but you will have to take it quite easy cos this is LOW
secondly, alot of people forget that the front splitter is no where near the lowest part of the car, if you lower it so it fills the arches the sump guard is probably another inch to inch and a half lower than that, so go carefull...
if you wanna go low invest in some decent adjustable coilovers which will lower the car to your desired level but you will have a decent amount of comfort...i.e KW variant 2 or 3, H & R coilovers
up to you bud, but im lowering mine 25mm, still got the looks, but you have more performance than if it was lowered 30mm