My comment is towards letting it warm up to operating temps prior to drive it at all. Both of my cars are up to operating temps 5 miles down the road.
The overall goal in the mpg world is to get as much as one can, not just accept it going down because another "thing" causes it to decrease.....
Panama City, Fl
2011 Mustang GT California Special
2000 F250 SD 7.3 Super Cab