I find my 18" tires on the M3 roll up faster than the the forged Neez 19's and tires.
I think the tire weight and rotational inertia play a big role and 20" tires will be much heavier than 19's. I suspect the 19" wheeled car might be faster on the track. Driving day-day it might not be measurable.
My thoughts only anyhow.