there is a discussion on big skimmers right now, and a guy with a 4848 uses a reeflo pump on it. he claimed to tried a pressure pump, and the reeflo pump worked better.
on normal single Beckett, pressure pumps are better. but the MR6R is a multi-Beckett so i would do what the manufacturer recommends.
also, what is the thickness of your acrylic? if its above 3/4 then MP40's are out of the question.
apon feeding your skimmer, i would use one of those 4 bulkheads and run a gate valve and go straight to the skimmer. (no durso or anything... this way its always submerged and you can regulate the flow by using the gate valve.. plus gate valves are more precise which will help you dial it in)