I use several in my SPS dominate 120DT. The bulk of the in-tank flow is handled by a pair of Gyre 250's mounted on the back glass on either side of the overflow. They are ~1/3 down and angled up a little, max flow @ 70% to avoid waves cresting over the front.
I also have a pair of Koralia 1500gph joust above and to the outside of the gyres. They are pointed up and towards the front center.
In addition to the 1500's, I have a pair of Koralia 850's on the sides just above the sand so that there is good flow in back of the reef.
A eheim 1262 provides return from the sump. I figure that when everything is going at once I have around 80x turnover, but with the gyres and 1500's on controllers it probably averages 60x or so.
Regardless of how many power heads you have, the goal is to prevent dead spots where detritus can accumulate while providing adequate flow for your particular system.
What size tank and which jebaos? What are you plans for the tank? Both will help decide what you should be aiming for.
HTH!
