We went from 2 2388s to a class 7 lex, and a 2388.   Our harvest window is usually from Sep 10 to Halloween, but sometimes can squeek through to thanksgiving (usually not ideal in Nov)

In corn, we run the 575 with a 12-30 with a must have grain cart.  The 2388 now goes off to do the neighbors, unless the corn is 15%, then we harvest allot of corn in a day.  Last year we were done picking on oct 13 as most our corn was 13% (drought in july made corn dry and aroun 170 avg)

Where you farm my play a major role if you can go to one combine.  Weve ran 9600's in the past, no doubt a 595 and 40' headers will out do what ya got now.  Not saying thats good or bad, it is what it is.   Weve battled the same decision your facing.  We custom cut around a 1000 acres on top of our own for the neighbors.  With a big machine, it would only run half a day at best because of bottleneck dumping facillity's.   Anyhoo........If your south or west of us, I'd say its a no-brainer to go to one machine, but if your 9600's are in good shape, you obviously know em in and out, they are a good machine, ya might want to consider runnin em till death.............IMO: 7.31 corn isn't good for anything in the long run.