You don't need a Z rating. H is fine if you're staying on public roads. Z isn't even as high as other ratings: I think W and V are higher. Also, you can run a bunch of sizes: 205/55, 215/50, 225/50 and others will work.

-Philip Maynard '95 Contour [71 STS | Track Whore] '97 Miata [71 ES | Boulevard Pimp] 2006 autocross results