OK, I went with the 18"s. No regrets. It rides nice, a little harsher over manholes and such but nothing like I was afraid of. Looks great too. I'll post pictures as soon as I get it cleaned up.
One question: My old front tires had "cupping" on the inside. I had three different tire shops look at it. One of the better shops in town said it was out of alignment. The other two said bad struts and that alignment would wear even. Would struts (shocks) go bad after 57K miles? Any thoughts?