...A Lot of Theory going on Here. I only deal in Proving the Facts!
First, the Shuttle valve does a lot more than Just turning on a Light!! The first time You Blow a Brake Line, You'll Know, It just saved your Life, by Closing-off the Damaged System (Fronts or Rears), and Leaving the Remaining Operating System, to Fully Function.
The 'Proportioning' Valve Limits the Pressure to the Front Calipers, It is My Opinion, By Test, Remove that 2 Pound Piece of Junk, and Throw it as far as you Can into the Dumpster!! Just by doing That, Your Front Braking has Improved. The Photo of the Rear Brake (4-Piston Superlites, 12.5 x 1.250 Rotors), was taken After I Returned from My trip to the Deserts. There are Approx. 3000 Miles on this Rotor. They are Polishing-In, Perfectly. On the Front Brakes, I installed Scotts' 6-Piston Calipers on (Pantera East) Thicker, Vented and Cross-Drilled, Rotors. By Installing the 6-Piston Calipers....Perfectly, This alone, Increases Pressure to the REAR Calipers!!
The Truth is...I have Done Brakes and Custom Machined Brake Installations for Over 50 Years! These 6-Piston Calipers are the Finest, most Responsive Brakes I have ever Experienced! The Most Tight, Up-to- the Top, Pedal. Smooth Solid Pedal Feel. You Actually 'Receive' MORE Braking 'Action', Than You 'Ask' For!! I have Never Experienced Breaking Action as This, In ANY Vehicle. They Bring My Pantera Down From Speed....FAST, but Smooth! And when you Come to the Actual, Final STOP, You Experience That Wonderful, One-Single, 'Lamborghini', Blip, of the Nose. You Only get this 'Jounce' with Stiffer Aftermarket Shocks, But, It Takes the Calipers to Perform it. It's the 'Last Millisecond of the Rotor Being 'Locked' to a Stop!'
For a 'Road Car', the Pad Compound is PERFECT! They wear-in Fast and Smoothly, I have Yet to Hear a Single 'Squeal'! I Do Not have a Photo of the 6-Piston Installation, Yet.
Last, Notice the Rear Calipers have been relocated Forward of the Half-Shafts. And, the SACC Parking/Emergency Brakes Have Not been installed yet. Most All Exotic Cars have all 4 Calipers Mounted Closest to the 'Center of Gravity'. This Decreases the 'Polar Moment of Inertia', as well as just being a better Engineered use of the Physics of it All!
...Stay with the Stock Brakes?? Fine, if You just drive to the 'Grocery Store', once a Month; or Your Pantera just sits in the Garage, and You come out and Look at It every once in awhile! But! IMO, You will NEVER Know What You are Missing!
But, if Your into 'Spirited Driving', and Breaking Speed Laws, Once in awhile….Get New Brakes. I will 'Bet My Pay-Check', You'll be Happy You Did!
For the Road, These are the BEST by TEST!!
Good Luck with it