I just switched to that from IO, so I don't have a comparison, since I haven't mixed any of the RC yet. In other words, I am at a loss, other than better surface ripple (gas exchange), but it seems you have that covered. I used to have a lid, even with the "punch out" plastic punched out, I couldn't get a higher pH.
Do you actually have a lid or are your lights suspended over the tank. I know you answered with, "I keep the top completely open", but I'm not sure if that means no top or a cover with the "punch outs".