You'll get a NOTICEABLE difference with PIAA superwhite bulbs but, don't expect that much. The standard lights on the new C's are excellent to start with. The colour is a brighter whiter white than most to start with. There at least as good if not better than my fathers '01 S40.

__________________
1989 300CE - 269,000 km
1994 SL600 - 59,000 km