The B777 had to have a few modifications to it to be able to carry the same load and be more efficient as the MD-11 like 2 115k thrust engines as opposed to the 2 90k engines on the original -200. The MD-11 has 3 62k engines and as stated above can be easily ferried with one out.
Actually if you want to compare the 777F with anything, you'd be better off with a 747-400BCF. Both are able to lift around 107 tons, but the 777F can carry the load further. Given a similar load, say 75 tons, the B747-400F will burn 140ish tons on a specific Far East - Europe route. On the same route, on the same day, a B777F carrying the same 75 tons burned 100ish tons. And therein lies the reason why the B777F is the best thing since sliced bread in long-haul cargo, as long as you can live without a nose-door.