It seems to have helped me to go from a 50:50 ratio of 6750K and "actinics" to a 25:50:25 ratio of 6750K, 10,000K, actinic. I also have 8 W per gallon (over a 55 gallon) and would not recommend any less light than this. I also have them up high on some shelf rock. All my corals, as well as these clams (corcea) seem to have appreciated that light ratio switch. It looks better too IMO.
Having said that if I were to do it all over I would have them under double-ended HQI halides, which would probably cost no more than I have spent on the compact fluorescents. Two 150 W bulbs would actually be a little cheaper to run I think.