Odd, I swear I wrote a reply to this one last night... Ill abbreviate it.
1. what amount of turnover are you planning with this? to get just 10X flow, you need at least a 2000GPH pump. I would only go with a non-submersible pump.
2. Given the ammt of flow needed for a tank your size, I would highly recommend a larger diameter of at least 1" outlets. 2000GPH thru a 3/4 outlet will be very forceful as opposed to a 1" outlet which will be more turbulent and less direct. in the reef tank, you want this turbulence as opposed to the direct flow.
3.Be careful throttling the pumps back. starting is hard on an electric motor as is not providing it proper voltage and amperage. you will wear the motor out prematurely.
fwiw, on my 180, I have a reeflo dart rated at 3600 gph on the closed loop. it has a 2" intake and 1 1/2" discharge. I run 1 1/2" all the way to the tank where it splits to 1" in then to dual 3/4 lockline nozels. I will get alot of force thru them enough to impact the other end of the tank.
I would strongly recommend you revisit your flow and plumbing size. if you choke the intake down on a pump, it will cavitate leading to bubble issues. Look at maybe more outlets and an ocean motion or sea swirl device. I use a pair of the latter on my sump return and love them.
