14 mm seems on the small side , The R6/R1 calipers i have just taken off has a16 mm master cylinder but would be better with a 17mm. What is the size of the master cylinder fitted to the GSXR 1000/ Hayabusa fitted with the Brembo calipers? These have 4x 32mm pistons.
I agree 14mm does seem small but that is what is cast in to the side of it for my 2008 front end. ( the Haynes manual and various rebuild kits also confirm 14mm on the 2008 and later bikes )
Don't forget that the lever ratio also has a big part.
You can have a very high fluid ratio but calm it down with a low lever ratio.
The brembo style radial masters only have an 18 or 20 mm lever fulcrum point.
They rely on a larger piston being moved a small distance for braking.
The std Hayabusa uses a 27mm lever fulcrum point.
It relies on a smaller piston being moved a longer distance for braking.