Will spoil the handling, will tramline, acceleration will be noticably worse, will be expensive.
i get 205/40 17 goodyear eagle f1's for £72 each so price isnt an issue.
Have had 17's on now for about 2 years and I still love my car! out handles most things - dont get me wrong it could be smoother but I think they are a good compromise between looks and performance. mine is lowered approx 50mm on H&R coilovers and imo its great - could do with the suspension setting up a bit better but its in no way unbearable.
the 197 has 17's, mini can come with whatever size you ask for from the dealer - if there was that much of a problem why do they use 17's?
it tramlined on 16's too when accelerating hard so ot much difference there - I dont really get any extra tramlining
and as for poorer acceleration - thats rubbish! by the time you get a lower profile tyre there is very little difference.
The clocks are out on all cars so thats not an issue - if you ever use a GPS type device in your car you will see that the clocks always over quote the speed you are actually doing. when doing 76mph on the dash clock I am actually doing 70mph in reality - this did not change when i changed the wheels