I figure about 30x turnover for a mixed reef, w/ sps being in a higher flow area. For a SPS dominated tank I'd go as high as 60x turnover. So, your looking for something around 1200gph for turn over. I'd go w/ 2xkoralia 2's at least. I feel that flow is often under utilized, you need to realize that water is basically used for coral respiration. Also as you increase light you increase respiration, and thus need to increase flow. As long as your corals don't look ticked off put as much flow as possible into your tanks.