I dont think its over kill perse but that is a lot of light. If your using 14,000k-20,000k bulbs though I think its still on this side of sanity provided you can mount it a good 10-12 inches above your tank and provide good ventilation so as not to have excessive heat or evaporation issues. This would work out pretty good for SPS and Clams such as the T. Crocea and T. Maximas. It might be a tad bit much for most LPS and a majority of soft corals though.
Another way to acclimate corals to intense lighting when upgrading is to go to the hardware store and pick up some screen from them and cut 3 pieces the size of your tank top. Place all three on top and run a slightly abbreviate light cycle the first couple of days then the regular cycle the remaining 5 days of the week. Then remove one of the three screens. Each week remove an aditional screen untill all three have been removed. This might prove a little easier than elevating your light and lowering it. Either way both techniques work very well.
For what its worth, my 20H currently has 2 x 65 watt PC Actinics and a 250 watt halide with a 12,000k bulb mounted in a DIY canopy with a ventilated top and no fan, 6-7 inches off the tanks surface. My only real issue is that I do loose about a qt of water a day due to evaporation. As far as heat goes my tank will pick up one maybe 2 degrees extra when the lights are on, but with 380 watts over head that close to the water that aint bad! With the exception of one Fox Coral, one Acanthstrea Lordhowensis and two colonies of Zoanthids (all carefully acclimated to the intense lighting) this tank is SPS corals and Crocea/Maxima clams.
Now for the discliamer...My canopy is quiet unconventional in design and I put a lot of thought into it before I built it trying to take advantage of heats tendency to natrually rise. The large open areas to the back of my canopy coupled with a expanded metal mesh top does an excellent job without the benefit of fans of creating a daft to remove the heat from the canopy. YMMV.
