60mm is the point where speed bumps become a problem and the ride becomes harsh. You decide what's practical, but personally for daily driving 40's low enough for me, also with my wheels without cutting the arches out completely I haven't a choice. Handling wise, it really doesn't make a massive difference - some people equate a firm ride to better handling which isn't the case. Suspension geometry wise the lower wishbones are level with a 40mm drop, thoeretically good, but the lower you go the further out of design spec you are going, not that it makes any real difference on the road.