i have the sea swirls and i have used them with vortechs on my 290g which is 7' long. you will probably benefit from using both. i had 3 vortechs but i switched over to Tunzes because of the constant humming from the vortechs. it all depends on what type of corals you are going to keep......sps then more multiple units, lps you could get away with 2 opposing each other.
How big is your return pump...two 1" returns is a lot of flow...two 3/4" should be fine (and less $)...2 1 inch seaswirls kinda centered in the middle...