I am after both performance and mileage even with a 550i. Why waste money?

 

Well the 17/25 spec is outstanding for a car w/400hp & 450 ft-lb torque and weighs 4300 lbs. I've haven't seen any other car with those types of numbers get anything close to that.

 

Real world numbers are generally lower than the EPA estimates, as you've seen already with your 15 to 18 mpg return to date. Those numbers probably won't improve markedly as the car ages (they may even deteriorate given that you're probably driving the car relatively gently during break-in) unless your city/highway driving mix changes. EPA numbers are a guide, but they're rarely close to reality. FWIW the current TL gets an 18/26 EPA estimate. The EPA changed its test methodology in 2008 to try to address the disparity between the theoretical and reality numbers but the problem still exists.

 

After the engine is fully broken in, mileage reportedly improves.

 

Reportedly so, but I've never seen much of a material improvement on any of my own new cars, BMW or otherwise. The engines will tend to loosen up (in a positive way) after break in, but any improvement in gas mileage tends to be relatively marginal. My own view is that any material difference in post break-in MPG, either positive or negative, will most probably be more attributable to a change in driving style or changes in the urban/extra urban mix compared to the break-in period.

 

I agree on the EPA estimates versus reality, but that applies to every car... The 550 still gets pretty darn good mileage given the power of the engine!

 

Yep...that's my only pet peeve, I wish they would put slighty larger tanks in the 550 so we could squeeze a little more range. Something like 410-420 miles would be awesome for me!

 

So true - I totally agree - ironically the new Mustang gets pretty good fuel economy must better than the 550. I would love to have a 550i -because the car is such a beast.