Just curious. I was looking at my side sills and thinking just because they're flared are they more aerodynamic than the SE's. Plus the M5 stands taller than the M sport!! Whats that all about then :confused:

M sport package tends to increase downforce for better grip at high speeds.
This is likely to make the car fractionally less aerodynamic, think of the effect of race cars, when they 'add' wing, they lose some straight line speed but improve cornering.

I believe the M5/M-Sport side skirts are designed to deflect the air more efficiently past the wider rear wheels of the M5. On a lower-model car (e.g. a 525i), I expect this isn't necessary, so doesn't improve Cd, but on an M5, with 285 wide rear tyres, it probably does.

The M5 stands taller primarily because of the bigger wheels, I suspect.

Correct, my ACS improved downforce stability - I did notice however a drop in high speed acceleration ( >220km/h).