I personally like the shimmer of MH. But T5's are great due to electricity savings plus you can mix/match color as you like. I think 400w are overkill except for the large SPS tanks. Plus you'll be sucking down huge amounts of electricity. Consider a balance maybe? 250w halides are great, but you could very well go with 150 or 175 halides, and supplement with an array of T5's. That way you get the best of both worlds. For my 125 long I am going with 3x 250w HQI supplemented with T5's (actinic/blues + pinks) for supplementation. I will use the T5's to transition morning/evening to simulate sunrise and sunset. Don't have to use actinics for T5's though. Easy enough to toss on some extra 10K daylight T5's to boost PAR over the halides too.