18's would be awful. You would have to run 213/35/18's which are not only fairly big but are very skimpy on the sidewall too. The results would be that your car would tramline (due to the 215 width), it would accelerate slower (as the rolling radius is larger) and you could easily damage wheels due to the lack of sidewall protection.

I used to love the look of my car on the 17" white multispokes, but changed them in favour of what I now have (which I dont really like), purely because it made the car drive much nicer. I can't say I wont ever go back to 17's, but 18's are a definate no-no in my book.

Aside from all that, you choice of 7x18's is fairly limited........