I woulda thought that 30-35mm would be fine...I had my mk2 sat 40mm and my mk3 and both were fine with that...the mk5 does fill the arches better than both of those as standard so if it's not for handling improvements and purely looks,coilovers would help you get the stance you want.
If the speed bumps are not the full width of the road, appraoch slowly and ease up just one side of the car that way themiddle won't be in contact