540's catch a lot of people off guard...they don't expect them to be as quick as they are especially at highway speeds. When my M3 was stock I had to be careful running a 540 because they have a nice torque curve and are generally automatics which makes it easy to smash the gas and go. They can easily give an E46 M3 a run for the money in the 60-120mph range if the M driver isn't on point.

 

i think next the the 335i, the 540's are one of the biggest bmw sleepers ever.

 

I thought that too but I think the 335 is becoming less of a sleeper. I beat down a C5 vette the other day and got a chance to chat with the driver at the off ramp...he said that he didn't expect to win when he saw it was a 335. I tried to soften the blow by letting him know that I was putting down around 420 RWHP.