I ran a dart on my 120. Wicked flow. Closed loop is the way to go unless you have a monster sump. And, you actually can have too much flow, but most people tend to not have that problem. However, if you go with the dart and run it closed loop (which I would suggest), then you will need another pump to feed up from your sump. And if you run the Dart CL, then I doubt you will have significant head loss, in which case you might end up wanting to cut back the flow as some others have suggested. Word of CAUTION
though, if you end up cutting your pump back a third, you run the risk of burning your pump out. Not the kind of money I would "waste" on a nice pump.
I know you want high flow for your sps, but your clams will absolutely hate you for it. You'll be looking to make calm pockets you can stick them in, but if you have tons of flow blasting through your tank, it might be rather difficult. HTH