Will the only source of water movement be the seaswirl(s)? If so, you should probably have two of them on opposite sides (ends) of the tank.
What kind of corals will you be keeping? If you will have corals that like high flow (and the seaswirls are the only source of water movement), you should probably use two 3/4" seaswirls for a 60-gal tank.
You could also get a eductor from aquatic ecosystems and just run one sea swirls. The eductor attaches to the out put and for every gallon pumped through it pulls in another 5-6 gallons and shoots it out too. This is what I am considering for my tank its a 75 gallon. that or the wave 2k surge device it pulls in 4 gallons and push out four gallons at the same time alternating top and bottom flow in the tank. Its in the marine depot catalog. HTH Steve
Just remember that an eductor doesn't create energy - it just converts a small volume of high-velocity water into a larger volume of lower-velocity water. So you need a pump that can deliver high-velocity water (pressure!) to the eductor. If you don't have enough pump capacity, it will not work effectively.
No. The smallest eductor at aquatic ecosystems (mentioned in one of the above posts) recommends a minimum pressure of 10 psi at a flow rate of 7.5 gpm. A maxijet 1200 maxes out (zero flow) at about 3 psi. At zero pressure, a maxijet 1200 puts out about 5 gpm.
So, converting what they recommend (psi and gpm) into what we are more familiar with (ft. of head and gallons per hour), you ideally want a pump that can pump at 20 ft of head while still producing 450 gph.
In reality, you could probably go down to half that much (say 450 gph at 10 ft of head, or a SEN900 or MagDrive950), but the results would be significantly less than what the eductor is capable of.