European Car magazine recently did a test of after market brake kits.
I think it was for a Subaru WRX or BMW. Overall, the aftermarket brake
kits stopped a bit shorter but overal braking distances did not shorten
all that much. The big difference was in repeated braking and track
driving. The stopping distances would increase on stock brakes but
the large aftermarket kits could take the repeated use. You might
try to track down the issue. I think it was in the past 4 months.

I believe some AWD models get larger front brakes. Also, the police
package for 850s has larger front brakes. So, the OEM components are
out there.