I put a larger diameter tire on all wheels on my car, I went up one profile - same width.
The wheels fill the arches better - no rubbing from the rear, just a bit on the front every now & again when I'm on full lock, and then it only rubs the splash shield. Do a search under my name and you'll find the post which has a pic on it.
Ride is a tiny bit softer due to the taller sidewall.
Speedo is out about 2.5mph @ 60mph.
Spoiler comes up at 65mph now, consequently goes down at a different speed to normal.