are you looking for an internal pump or external pump?

your choice really depends on how you set things up. you want slow flow through your refugium section and a bit faster flow through your skimmer section. do you plan on feeding other devices with this pump (ie calcium reactor, phosphate reactor, chiller, etc)? if so, you can go with a larger pump.

on my 180, i'm running a mag 9.5. i have very low turnover through the sump which is what you want.