Not sure about open loop myth, but the ECU does run it a little richer to bring the temp up to where it thinks it should be. You can read all about it in the Ford Fuel Injection and Electronic Engine Control.
Mostly it affects things at part throttle cruise, when the CTS sensor sees not enough temp. And it will affect MPG since it's running richer than normal.
Ganzey, not sure where you read 200-220, and what does that mean? Is it oil temperature? Or coolant temperature? Oil temps are typicaly under 300, 250-285 is what I see on the oil temp gauge during a track session. And depending if you have a oil cooler or not wil affect this, plus a few other things.