Cough,
That's all good, but EPR measures the difference in pressures between the intake end and the core exhaust, not the fan exhaust.
I believe a big "contributor" to the decline of the EPR gauge was that more of the "thrusting air" is now coming from the fan instead of the core (ie. fan speed is a more relevant indication than core pressure differential). For instance, a takeoff power setting on a JT8D-17 is around 2.17, while on a -217 is 1.91. The cores are essentially the same on both.
What would be useful is what is only found on the RB211, an IEPR gauge which takes a combined reading of core and fan air pressures.