[rzm3]

Got these from Sport Auto. It's pretty amazing that a magazine would spend the money for these data.

Anyhow it seems that the aerodynamic improvements on the M3 are actually quite significant:

Front Lift @ 124 mph:
335: 42 kg (93 lb)
M3: 10 kg (22 lb)

Rear Lift @ 124 mph:
335: 28 kg (62 lb)
M3: 23 kg (51 lb)

Note: these cars do not have the aerodynamic devices to actually create down force.

It is pretty amazing that M3's front bumper and some lower body work reduced the front lift by 71 lb. Looks like M3's rear spoiler also works.

Also provided is a comparison between 911 S and GT3 RS. To create down force you need real wings, splitters, diffusers, etc.

Why is the Gumpert Apollo so fast? Just check out how much down force it can generate.

Finally, one may ask why not give the 335/M3 more down force? The answer is that down force comes with its price -- drag, which reduces your fuel efficiency. Super car owners don't really care about MPG, but for a regular street car like the M3 it matters a whole lot, especially in this age.