MAH's summary is fairly accurate.
The LR's operating costs are fairly similar to the ER's. slightly better than the ER because of the wingtips and the improved GE engines. AA and DL use the same engine on their 772ERs, thus the comparison of what the ER does relative to the ER is valid for both airlines.
The LR's engines are slightly derated over the 300ERs but the LR still has enormous cargo lifting capacity as well as performance.
Just to give you a comparison of the difference between the 200ER and the LR, a couple years ago, BOM did runway construction and closed 2000 feet of the runway, leaving the runway with just 9000 feet.
CO operated their BOM-EWR flight with the 200ER with GE engines. DL, which flew to JFK at the time, operated with the LR and added the LR right before the runway construction began.
DL operated the route with no weight restrictions while CO had to block significant numbers of seats and/or make enroute fuel stops to cover the 8000 miles to NYC.
DL also used the LR on DTW-HKG while UA/CO used the ER on EWR-HKG and at times ORD-HKG. DL carried about 25K more cargo per DOT stats than EWR or ORD carried
DL and UA also operate the LR vs ER on LAX-SYD. DOT data is not available since UA made the conversion but Virgin Australia is one of the highest cargo carriers per flight with the 300ER while DL is up there with the LR. UA carried very little cargo on the 744 and is not expected to be able to carry much on the 777-200ERs that they use.
The LR is an enormous performance machine.. but it is not cost competitive with next generation aircraft on routes where those aircraft can operate.
AC and EK both use both the LR and 300ER and prefer the 300ER when they can use it based on more favorable economics.
