Personally, I like the torque on my M5 better than the 540 as well, but generally speaking the 540's torque falls into the "daily use" category more than the M5. It probably comes down to personal habits and preference.

Having owned both, I can actually put the numbers higher than the EPA rating. My M5 is a solid 16/21, and that's driving like a maniac. Granny shifting gets even better results. The 540 was probably 22/28. If you're getting 12/19 and 14/21, there is probably something wrong with the car.

Borla, SuperSprint, and DINAN are probably the top three.

Only a few models have the XXXiT badge; most just denote the i for fuel injection.

A few other things I think should be noted: