Welcome fraser, nice to meet you, 2 600s aren't much, but it really depends on what you want to keep in your tank, I'll tell you having enough or too much flow is something we all have questions about, Some Corals want low flow, some want high, some stir up the sand bed, some don't hit those stagnant spots in the tank, It's all a matter of trial and error and what suits your needs, I hope this helps.