you don't necessarily scrub when you increase your wheel size, if you decrease your tire profile appropriately.
Not sure about older golfs, but when talking possible mk4 wheel sizes... 195/65/15's, 225/45/17's and 225/40/18's all have nearly exactly the same total diameter ( about 636 mm ).

I'm personally not sure whether to go for the 17's or the 18's for me mk4. What do you think??
Rich