See... I would tend to disagree with that for the most part but every situation and use is different. In my last system, My wb5000 fed...
- display tank which was an oceanic tech 90 with 2qty of 3/4 returns
- 10G display fuge with enough water that I ran it as a silent / siphon return
- and a 30G frag tank which also ran as a siphon return.
If I had all that directed into a single tank, even my 225 with dual 1" returns, it would be PLENTY. The qty of nozzles should not matter much as the goal of a proper return system is not to generate flow within the tank (unless it is designed specifically to do so) it is simply to circulate water from the sump to the tank and back so that your skimmer or other items can clean that water. But again, maybe this person is trying to do a seaswirl or similar, maybe even a closed loop so will see what he has to say as the situation and recommendation could change drastically at that point.
Another little hint that I dropped long ago and I MAY be incorrect on it, but after owning both, the 5000 and 7000 appeared identicle. Only difference was the impeller

So one could possible make it either

But do not quote me on it as I did not try it. I have been meaning to put a 7000 magnet and impeller on my 5000 just to see how it goes but have not had the need to do so.