if you fit 17'' wheels on your car i presume you will probably fit pretty low profile tyres as well, this will make the ride harsher than what you have probably used to.
buildersmate i dont pay a great deal to insure my car anyhow been driving a long time so that wont worry me to much, yes tonyav think i will have to have low profile tyres.
it will tell you how much it will effect the speedo in both speed and percentage.
if it's too much different it will effect other things too, a significantly larger rolling circumference will put a lot more load on the brakes and you may have problems with clearance in the arches.