I flew a PHL-LAS 757 segment about a year ago and an MEL item (I think it was a spoiler, but I don't really remember what it was) kept the airplane from operating at its normal takeoff gross weight. The flight was full, so the only way to get the takeoff weight down to the restricted number was to leave fuel off. We planned and executed a fuel stop in BNA. Those station folks had never seen a US Airways 757 there before; the station manager left a meeting to come out and make sure we got serviced promptly (and, I suspect, to see the airplane.) The did a fabulous job and turned the airplane in about 25 minutes landing to takeoff. The passengers were not happy about the whole thing, but we got to LAS less than an hour late anyway.
The point being: the 757 has no problems with a full load getting from PHL to LAS, unless of course an MEL item keeps it from operating at its normal gross weight. Then a fuel stop is almost inevitable.