so u want 6 pot brakes on the front running between 330mm-345mm and leave the back standard?
like i said the bios would be horrible
standard fwd cars (according to google) use a 70%-30% braking bios, i wouldnt say 30% is "hardly worth doing". if your going to muck around with something as important as brakes, do it right!.
It shoes how little you understand braking systems. Brake bias is set at 70-30 for initial braking, if you are braking hard that bias will change to 95-5% due to the weight transfer to the front axle (the braking system reduces the bias to the rear to stop the rear locking up, even with ABS).
Brake bias is set to 70-30 as it slows you more effectively under normal conditions, but when braking hard (when you notice the benefit of better brakes) so much weight comes off the back wheels you can almost ignore the brakes.
Having too much rear bias would lock the rears or kick the ABS in, increasing stopping distance.
Upgrading rear brakes alone is pointless but fronts is a non-issue.
As for changing master cylinders, it only boils down to the ratio between master/slave if you go from 1:5 (say) to 1:10 of much larger slave cylinder area then you will likely have excessive pedal travel and will want to upgrade the master cylinder to a larger bore.
Fitting larger discs with standard calipers would require some way to move the calipers out and even with standard line pressure is effective because you are moving the centre of pressure further out from the fulcrum creating greater leverage on the wheel.
Lopez speaks the truth and I also have driven cars with heavily upgraded front brakes (even my kit car had 4 pots on the front and stock sierra brakes at the rear) and it is a non-issue.