The E49 M5 also has fairly underrated brakes for the size and speed of the car, but they are perfectly adequate for normal road use. Only track sessions or pretty extreme driving on the roads would cause fading. It appears (from the autocar article, which i trust) that the E60 suffers from the same.
Im pretty sure that the fact that it is only twin piston calipers on the front has nothing to do with the brake fade, that is purely down to the pad composition, and the effective cooling area of the brake discs. And the discs are monsterous, so im guessing that a simple change of pads to a harder or carbon metallic compound would cure the fading problems, for track days just they'd be a bastard on the road.
Bear in mind that the tests of the E49 M5 complained about fading brakes, and the Ring Taxi runs different pads only, it does get through them, and discs rather rapidly though!
