I had 8.5x18" with 215/40 profile tyres on my toyota carina, together with some stiff shocks&springs. it was a pretty hard ride. but it took a bit over 2 years before I started notice any vibrations in the steering wheel (i.e: the wheels needed balancing again 'cause of the abuse).
I ran 8.5x19" with 225/35 profile tyres on a '98 golf I had. in just one summer, i started feeling vibrations through the steering wheel.
ride quality really isn't that different between the two. the 35's felt a BIT harder. but you can do a lot with springs and shocks/dampers to soften it up. but what you got to realise is that your rims won't last 5-6 years. so i guess it's a matter of how long you're planning on keeping them.
btw: if you want to keep the correct rolling radius (or whatever it's called) on the wheels - the celica should have 40 profile tyres with 18 inch wheels (as far as I know...). 35 profile is for 19's.
and I havn't tried 30 profile yet, but I've asked a store selling rims&tyres about them - and they said I should be prepeared to get my wheels straightened out once every 2 months or so 'cause of the abuse they'll have to take with so little rubber.
