Just purchased a new set of winter rims and tires for the Q5.
The existing rims are 20" and my tire guy recommended dropping down to 18's as the prices for 20" rims and tires is much more expensive. I was really happy with my winter Continental's on the A4 so I went with them again.
I went with RTX OE Nuremberg's in gloss black, with Continental Viking Contact 7.