There are a lot of factors involved in coral growth and calcium carbonate solubility, both of which play into how well corals grow. Given the limits of hobbyist testing equipment and our ability to control all the parameters involved, trying to find an optimal level is going to be very difficult. There are some studies (as already noted) that increasing the calcium and alkalinity levels can encourage growth. That said, growth isn't our only goal. Personally, I suspect that 7-11 dKH, the usual recommended range, is going to be close enough to optimal for most tanks, although carbon dosing sometimes seems to make higher levels in that range problematic.
Coral coloration probably is of more interest, relatively, than absolute growth, and it's less well understood.