Is it possible you'd get a slightly better range because of one less engine. Just wondering...
Yes, for the 737 that is the case.
If you look at the long range cruise tables at 10,000'. Fuel Flow is about 10% more for the 2 engine case.
Our company works on decompression (2 engine) as the most fuel critical scenario for ETOPS planning. They don't use LRC as the speed schedule, but the result is the same - decompression (2eng) is more limiting.
Establish planned contingency airspeed
For us, planned speed is simply that - planned speed to establish the area of operation. There is no need to actually fly at that speed if you had a decompression.