Edit: “At a GPM around 3-5, you really need an exit more like 3/4”.”
Have you already hooked up a valve to the cold water pipe and seen that you can get the flow you want? It would be a shame to do all this just to get the same flow.
I am on a well and have realized that I need to make seasonal adjustment to the regulator to get flow and proper shut-off. If the toilet in the laundry room is filling, you can forget about substantial flow from the kitchen sink, too.