IMO it really comes down to light spectrum and par.If your leds are not the correct mix then the coral will react to this.Some will open,some won't and others will just wither and die or bleach out.That's the hardest part of a DIY led fixture.T5's have the advantage of a company that has designed and tested this factor.Par and pur from quality LED's is hard to beat and cost less to run and bulb life is really not an issue and as you stated there's no heat issue either.On the other habd if your not useing a par meter to set LED's up chance are's you'll experience some problems.We run our 40 gal frag system on a led fixture and have sps,lps and softies with a par level of 325 on the shelf. I would recomend testing your led fixture to see if your not over powering the corals.LED's are the way to go in my book.