It's only just over 3% circumference difference actually, having had some time to look this afternoon. The only consequence seems to be the diameter will be slightly smaller so the overall gearing of the car will be lower - i.e. higher revs for a given speed and possibly higher fuel consumption and brisker acceleration at the expense of top speed.
Lower profile tyres may also give a slightly harsher ride and the car will sit around 10mm lower.
Have to say I'm not really that put off after all - I'd obviously go back to 55 profile winters when the time came to renew them, but they have about 5mm left on them so good for at least one, if not two winters yet......hmmmmm