Regor, to answer your question, YES, there can be a significant difference in the indications.
I suggest ppuners re-aquaint themselves with the accident report on Air Florida Boeing 737-222, N62AF, January 13, 1982. Immediately after this accident, a lot of airlines changed their procedures, shifting priority from using EPR to N1.
Admittedly that was then, things may have changed thesedays.