Accuracy measuring tiny fractions of a quart via the dipstick is dubious at best. Attitude of the car, how long it has sat before checking and oil in the tube all contribute to what the indication is. I suspect the oil consumption hasn't really changed.
Driving conditions will contribute as much or more to the consumption as such a minor viscosity change.
I hope you still had a drain pan beneath the car when pouring those five quarts through.