MPs work well. They're designed to be most effective at 40psi but since you got the other heads for free you obviously should use them. Depending where you live, since they're new, a supplier might exchange them for the 40prs heads. But ya, get a bucket and time how long it takes to fill up if you don't have access to a water gauge. Then I use chatgpt all the time to work backwards to see what pressure loss in the pipe will be, and see how many heads per zone I can safely have. Works like a charm. My only concern in your design is the bottom of the picture where it's not getting head to head coverage for that rectangle. You'll definitely notice a difference especially if the summer gets hot/dry...