I use a mag 7 on a 75 and I wish I did a 9 because i configured my sump differently with the return in the middle chamber with a t feeding the refugium. I got this idea from Melevs reef but it is really for a bigger sump like a 40b or bigger (mine is a 20 L) I wish I had done the normal setup: dump, fuge, return so all of the pump could be going back to the DT. Oh well live and learn lol.
You can go with a bigger pump and put a T back to the dump then a ball valve to back it down a little so you can get the flow to the DT you want. The flow I get into the DT from my pump is pitiful.
One other thing is the pump is kind of loud from vibration so for my next one I will be looking at a quieter one.