why would you want a larger Servo? what are you looking to achieve?
It’s for a disabled driver that is soon not going to be able to put as hard pressure down. The Mini clutch and accelerator is really good and the brakes are working brilliantly - completely rebuilt with all new cylinders etc... and are using sure stop discs and etc green pads (would prefer the minted though).
the brake efficiency is as good as you’d get or need, the brake pedal force could be eased.
incidentally, the mini has just been fitted with electric power steering and it’s just nice. Not over posted at speed and great on parking - about the same weight feel as my wife’s R56 Cooper. The wee car has sportpack 13” wheels so was very heavy at low speeds.