I'm a firm believer in the saying " if it ain't broke don't **** with it " .......but, I also believe in the saying " there's more than one way to skin a cat " !
that being said, you can definitely eliminate the 4th valve and run the system as you say. It's like changing a system from load sensing to pressure compensated in a matter of speaking.
Problem is like Coop said. The brushless motor and esc in a 4200 won't like a lot of start stop. And as he said keeping a slow speed and then ramp up when running a function would fix that but then you still need a prv to dump the oil off back to tank when no function is used other wise you'll have a heat issue.
I think the best thing you could do is replace the motor and esc. Install something that is capable and set up to handle a start stop type system. I think of RCP57 Volvo excavator he built. Pump only runs according to stick movement and that thing runs great!
Personally I don't mind the 4th valve set up and have no servo problems.....yet, now that I've said it.
