Ideally you need gauges to test the pressures the system is generating. IE: what pressure is the master actually putting out.
Lot's of variables here but a general rule is 1500 PSI in a panic stop should be a good starting point. The next thing to checkt is what's the caliper seeing???? The same pressure ( it should be. Next is putting a gauge between the pads and mashing the pedal.
Short of having the gauges one can look for deflection of the hoses and cailper brackets as the pressure is applied. If you see no movement then you probably have a master issue.
if you are getting good deflection then you probably have adequate pressure. Next thing to look at is whetehr the pads/rotors are glazed. ANd lastly you might try a set of pads with a more agressive compound. I had a 68 Olds cutlass with SSBS setup on it that did pretty much what your describing. After much hair pulling we installed a set of aftermarket "ROTOR EATERS" and the problem was solved. hope this helps

TIm