Mr Whippy said:Bigger brakes might not always be better.
If you need bigger wheels, that adds weight, and worse ride.
If they are heavier it's more mass to slow down too, and less good wheel control due to more unsprung mass.
Personally I think the ones on the 3.0i are pretty good. I've never come close to wanting more yet. I guess if you are really heating them up then bigger ones will make sense (because in this case the upgrade is small impact on weight etc)... but purely in an emergency stop situation, the tyres are the limiting factor from most normal road speeds! (when the setup is already very good, which it is)
Dave
I take the point about unsrpung weight but here we're talking about better brakes not necessarily bigger and within the same wheel. OP's post was about better disks and pads. I happen to have bigger disks and calipers but I'll bet the weigh difference is ounces.
That aside BMW must feel they are needed for 2 reasons 1) the 3.0 has bigger brakes than the 2.5 and so on and at facelift time they enlarged them on the Si to 330's which is what the upgrade does and I don't believe all this is just for brochures and cosmetics.