I think a 6 bulb T5HO would work as long as the bulbs are individually reflected. I have a deresa clam and a long tentacle anemone in a 37 (22" tall) with a 150W 14K metal hailde supplemented by a 24" blue T5HO. The clam has always seemed to do well. I had one spell with the anemone where he went flaccid for a couple of days and pulled his foot out of the sand a month or so ago. I did a 30% water change and he came back around. he looked much browner than before for a week, but has greened back up.
I have a 6 bulb T5HO over my 75 with a couple of SPS
that seem to be doing well. I'd have no reservations about moving the nem and clam to that tank if something happened to the 37. I will say that the 37 seems to be a little brighter than the 75, but that could be the color spectrum or the shimmer playing tricks on me.
LEDs are the future between the nice shimmer and energy efficiency as well as durability. It's generally recommended to change halides and fluorescents once a year, where I think the LEDs will last for several years. I think if my either of my fixtures dies, I'll seriously consider the LED