Danny rather than go to a 400 I'd consider a 250W HQI, you'll get almost the same amount of light (depending on the bulb/tube you choose).
As for getting your tank used to the new light one thing I did that worked well for me was suspend the lights above the tank, say 2 feed higher than you plan on having them for a permanent placement. Lower the lights an inch or so every couple of days until you have them where they should be.
Doug
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