The following engines are approved for the 757-200:
RR RB211-535-C-37: 36,720 lbs
RR RB211-535-E4-37: 39,610 lbs
RR RB211-535-E4-B-37: 42,560 lbs
P&W PW2037: 37,530 lbs
P&W PW2040: 40,900 lbs
To compare PW with RR you would need to know the correct engine model.
Comparing PW2040 with RR 535-E4-37 (almost same thrust) the PW would come out on top regarding fuel usage.
Ex.: GW 240.000 lbs, FL350, mach 0.8: The PW2040 uses approx. 220 lbs less (per engine) per hour.
