In my opinion, its a waste of time lowering by 30mm, (172s are 15-20mm lower than a dynamic) I originally lowered mine 40mm on APEX springs, but with 17s, it looks too high, so its now dropped 60mm on 17s and looks much better (see pic in "Other Clios" gallery)
If you want handling, then go for 40mm but if you want looks 60mm