Can you gain other efficiencies in your harvest? Are there any other bottlenecks that slow the harvesting? Can you squeeze an extra hour out of every day? Would switching to one combine help accomplish this?
There are two larger operations that I know of. Both run newer equipment and the same color of combine. Similar acres. Operation #1 runs one combine, usually one grain cart, but sometimes two and 2-3 trucks. Operation #2 runs 2 and sometimes 3 combines, two carts, and several trucks. Operation #1 usually finishes harvest before #2. Obviously #1 has found a lot of operational efficiencies that have escaped #2. Also, #1 simply starts earlier in the day and works later at night. They also do a better job of planning their cropping program so that they can start harvest earlier. This year they are adding a lot of storage and a grain leg, but dryer capacity is still a bottleneck early in the season.
I don't buy the if one is broke down, the other is still running argument, as your capacity will be cut in half. Over the course of the season, the downtime of two combines will probably be twice that of one combine, so there is probably little difference in how much gets harvested.
To summarize, I am in the camp that believes that operating one bigger combine more efficiently is better than running two smaller ones less efficiently. There are some operations, though, that need to run two or more combines at full efficiency and can do that. One operation I know of runs 3 2377's over 10,000 acres of corn and beans in 30 days. Lots of hill ground and terraces and high yields.
It is my belief, though that most operations find it difficult to run multiple combines at the same efficiency as one.
Brandon