thanks for the comments
the EPA finding is interesting i wonder how accurate it really is i suppose as I delve further into this I can maybe find out. heck could probably just add 100 pounds to the car and see if it hurts mileage. though 2% may be hard to measure conclusively.
here are a few more pictures of the M RH77 if you have driven the regular z4 you can see how the M differs.
3.2 liter M engine produces 330hp in the roadster
the M steering wheel its really thick with the red and blue stitching
the seats leather with big side bolsters and M logos
M gauges 8k redline !
we got the Nav its pretty cool it closes into the dash if you want for the clean roadster look also it closes when the car is off
13.8 inch vented and drilled rotors with 18 inch wheels
quad exhaust and led tails, (though those tailights are now standard on the regular z4 for 08 )
M side logo and clear turn signals.
thats most of the differences between it and the regular z4 it also has an aluminum hood and trunk and no sound deadening insulation on either for less weight.
we love the car we picked it over a porsche cayman S and a few other contenders the M just sounds better and feels better from a drivers perspective.