Just received my FugeRay 16" for my Fluval Spec V (5G). I think its perfect for low-light. Remove the legs and you will approach mid-light. It also makes the tank pop compared to the stock LED light assembly.
I think for any tank around this size, the FugeRay 16" is perfect. It's also clear that the Ray II 16" or 18" would be far too much for low-tech setup (unless all you're growing are mosses).