Tobin,
The spreadsheet I'm using does support both balance bar & tandem MC applications. The numbers it returns are nearly identical to Ron's spreadsheets when I checked it by inputting the same piston sizes & MC diameters that Ron has run for others in the past-- I'm only seeing a very small (<2%) deviation between my numbers and his numbers. The reason for the slight deviation is because the spreadsheet I have only supports a single CoF for both front and rear pads while Ron's has separate front & rear CoF inputs to account for the temperature differences. I still need to update my spreadsheet to account for separate front and rear CoF differences.
I could be wrong though, which is why I asked for a double-check on the numbers.
My current C6/C4 setup with no prop valve has a 69/31 torque split (which is good.) However, assuming street friendly pads with about a .43 CoF, a .875 OEM style tandem MC, and 100# of pedal input that's only about 1250# of brake torque... not very good at all, and that was my impression when I tried to run them in a manual setup. More aggressive pads would help but as you said that comes with a dust/noise/rotor life penalty. The hydroboost made them really work well though... wish I had taken some line pressure measurements when the car was still running to see just how much force the hydroboost was providing.