If your "plan" is to run a 6 row machine 24 hours per day to get the job done, what is your contingency plan when things start to go awry? 

We start out planning to run 12 hours but shoot for about 16 in practice due to the advantage of getting done ahead of  schedule.   If start of planting is delayed, the limiting machine can be double shifted and pick up another 8 hours of productivity.    I'm sure this will just get the other crowd all in a tizzy, but oh well....the next option is to go to the shed and pull out the retired, supposedly inferior planter and add another 12 to 24 hours to the day.  By the time it gets to this point, you've already had to face the shortage of operators, and that may have become the limiting factor. 

The point is that a relatively low value planter which is already depreciated to the point that it's not really loosing much value anymore is not a bad insurance policy to have against conditions which close your planting window unexpectedly, or against an accident or some other event which takes out your primary operation.