re EPR - the P&W engines use a single EPR based on core tailpipe pressure. This is a holdover from the pure turbojet days, when it made good sense - EPR and thrust were truly analogues of each other.
On big fans, however, the bulk of the thrust comes from fan airflow, and with deterioration over time, core EPR is no longer the best measure of thrust. RR recognized this and introduced Integrated EPR (IEPR), sort of a weighted average between fan exhaust and core exhaust pressure ratios.
GE & CFMI (BTW, rmm has the etymology of CFM right) use N1 for thrust setting, and most operators seem to find it superior for both operational and maintenance reasons.