I think a 16/31 planter would be a lot of planter for the acres that you are talking about, but timeliness is important.   Only you have enough information to decide if the cost is worth it.  If you have a lot of irregular fields, you can probably make the row shutoffs pay with that size planter.

As far as the combine, if you were only able to combine beans at 2mph with a 7720 and a 20' head, something was really wrong.  I would find out what the issue was and fix it or replace the machine.  Either way, you need to find the problem first.  Changing combines may solve the issue, but if there's some operator error involved, you won't be getting anywhere with the options you presented.  The newer machines are nicer to run, but the crops are worth the same out of either machine and a 7720 can be made to do a good job.  How much is the comfort worth to you?

Mike