when i had my mk5, i looked at the rieger kit which was just front splitter and side skirts. the rear bumper on the mk5 is quite deep so they didn't do a rear bumper as far as i know.
i think its sort of the same on the mk4 so u could, in theory, get the front bumper and side skirts only and see wot it looks like.
once the car is lowered more, the bumper witll seem deeper as its lower to the ground.
to give the illusion that its even lower u could always get an exhaust to come out from underneath the bumper.
heres my old polo, it had no kit and was only lowered 30-35mm. she could have gone lower but that exhaust would have clanged everywhere!! a subtle kit would have looked nice imo.
![Image](http://www.photodump.com/direct/Dan20VT/polo2.jpg)