Tire Size question

[Mitchell Segal]

Hello all, 

I have a 2001 A4 1.8T Quattro w/ Sport package, which came with 225/45-17
tires.

My question to you is, can I put 215/45-17 on this car, or will they be too
small.  I've calculated that their overall height would be about 9mm smaller
than original, or about 1.4% smaller circumference.  At 70 mph, that would
be about a 1 mph difference on the speedometer.

And before you start questioning why I would want to go to a smaller tire,
it's only because a good friend of mine has a brand new set of spares that
came off his Lexus IS300 (Bridgestone Re040 I think they are), which he'll
sell me for really cheap, if I want them.  

What do you think?  Should I go for them, or is it too big of a difference?
I would be replacing all 4 tires at the same time, so there wouldn't be any
issues with the ABS or the quattro diffs.  I am not a super agressive
driver, and I don't think I'll be going back to the track anytime soon
(although it was a lot of fun), so the loss of 10mm in width won't kill me
on the corners.

Anything else I've overlooked?  

I value your opinions.  Thanks.

Mitchell