Personally i think if you spend some time and money FULLY overhauling the oem brake setup you'll find it's perfectly adequate for anything your likely to throw at it....but it will mean replacing front seals, pistons, pads, discs, fluid... and on the back, shoes and adjusters etc etc..... iv'e done this to 2 standard brake setups lately and it really transformed the braking and improved the pedal feel no end.... a slightly larger disc size is not usually the final word i think
Regards