mbattles, if it is a Sfiligoi, you can't really get much better quality for a combo fixture. pretty sure they make t5/led, mh/t5, and solo versions of all of them and many variations and sizes as well. For straight LED, i was gonna go with the AI fixture as well, considering how sturdy it looks and how perfect the color is. if i had the money though, i would prob splurge on a Sfiligoi and go with MH/T5/Led or at least T5/LED. and mbattles, i would say YES please acclimate your corals slowly. i usually tell people whenever switching from any kind of fixture to something else, slowly acclimate, usually because the fixture you did have has somewhat used bulbs anyway, and you are switching to all new bulbs/reflectors/fixture. but from experience and from what many hobbyists have told me, goin from MH to either t5 or LED, you have to be careful. as long as you do it slowly, you'll be ok.
either lower the photoperiod and slowly increase it maybe week by week, or hang the fixture significantly higher than your MH was above your tank, and every week lower the fixture by an inch or so. or you can do both to be extra careful. either way, little to no light on corals will not just suddenly kill them. but way too much beaming light over them certainly can (or at least bleach them like crazy).