For our hondas, outside of cosmetics, there is no reason to go to larger 17-18" wheels. There aren't very many big brake kits for our cars to begin with, and the few that do require a larger wheel to fit are mostly overkill.

A lightweight 15x7.5" wheel is generally considered "optimal"; you'll see drag racers and autocrossers use 13" wheels on occasion (but finding tires in those sizes is a bit tough).

Now I know a lot of road racing hondas use 17-18" wheels, but on a road course, taller gearing is more important. Either way, as long as the wheel is light and strong ($$$), the worst that can happen (say you get an 18" wheel) is that you won't suffer too much of a decrease in performance.

I recently chose to "upgrade" to a 14 lb. 17x7.5" wheel for cosmetic purposes mainly.

Shingo