Mine seems to be the lone dissenting opinion thus far. I have driven the M3P with 20" wheels (mine) and 19" wheels (a good friend's). Have any of you guys ridden on windy roads and pushed the car? You don't feel that the handling is substantially better with the 20's? I definitely noticed a difference and prefer how planted the car feels with 20's. I did this experiment as part of deciding what my second / winter set of wheels/tires would be. I actually use the stock 20" rims for both my winter and summer wheels. The only difference is that I use the Michelin A/S 3+ tires on the winter set (which have been dynamite in up to 5" of fresh, unplowed snow). The roads in the NY Metro area are garbage and I have been driving on 20's since I got the car in late December. Yes, I AM careful to avoid potholes but I have hit a couple by accident with no ill-effects.
I really think that the whole anti-20" wheel bias is a bit of Group Think. If possible drive the M3P hard with both and decide for yourself. From where I sit, if I wanted maximum range and economy (with all wheel drive) I would have bought the Dual Motor LR, not the P. I am not going to diminish the handling of my M3P for risk of damaging a rim or two now and then...but that is just my thinking!