I think Boeing claims a "standard" OEW of 120,000# - don't have any idea what the OEW is for the various DL 757's but that's a starting point. All their 757's have 180-some seats, so call it 36,000# of passengers/bags and throw in 4,000# of freight to make it a nice round 40,000# of payload. We're up to 160K ZFW. Boeing's charts show a 4,100 mile range for the P&W engined 757's (still air) at that ZFW. Compared to the RB powered 757, that 550 mi further than the 535C's and a little over 250 mi further than the 535E4B's. Not enough to eliminate the possibility of fuel stops westbound in the winter but enough to make them less frequent than US' 757's would require on that same route.
Jim
PS - before anyone corrects my addition, I caught it right after hitting "Submit" and have corrected both the ZFW and the ranges for the various engine's.