You say the combustion is not as great as it's not 100%, so why is there unburnt gas/air mixture in the exhaust gas to begin with? Because the combustion even without an EGR system still is not 100%.
I have given a little thought here and there, but no real research, to moving the EGR bung to post pre-cat, as nitrous oxide is a byproduct of the catalytic converter. There is just the problem of cabron monoxide..
Anyway, as previously stated, the EGR valve is only operational in low engine temperature, starting, idling, and excessively high coolant temperatures. Basically all times you are wasting gas, it recoups a little gas mileage. I doubt the performance difference is there from EGR to non-EGR, comparing factory tune with EGR against same tune with EGR function disabled to prevent MIL, because there is no "performance" at idle or starting..
