A proportioning valve will not work. It only limits the rears without moving the needed force to the fronts. A balance bar with side by side master cylinders is the way to go with a smaller bore. Bigger diameter rotors, more cylinder area in the calipers, less in the master a longer pedal and balance bar all add to the good.
Look at it this way. If a 110 Lbs. woman stepped on you with the back of a flat. Then the same woman stepped on you with spiked heels. Which would hurt more? A smaller bore equals a higher psi. Smaller bore are the spiked heels!
Then again there's power assist brakes, but I think you'll like those spiked heels.
Ralphy