That makes three of us in agreement on 18" wheels (from a purely performance standpoint). Bigger than that and I think you lose too much tire sidewall, add to much unsprung weight and add too much rotational mass. Some sidewall is good, just think of it as a cushion for you shiny new wheels. Besides, by everyone has seen the
Geico talking pothole commercial, I'm sure you all want to avoid that.
I'd certainly go with Rota over Ruff, but as Soup already mentioned...to each his own. Enkei's are good quality for not a lot (compared to say Volk) of money, another to look at are some of the OZ wheels over at Tire Rack. I'm not excited about some of the offset & widths offered but you can't have everything. Oddly enough that's a problem that I have with some of the Rota knockoff wheels...not the quality that every forum seems to have "A friend of a friend..." nightmare stories of, but that some of the widths & offset combos aren't very well suited to the Z's & G's.