I will start off by saying I love my 4 gen 3 Radions over my 233 mixed reef tank.
But about 4 months ago I went back to mostly zoanthids in my 50 gallon tank. I also went back to a ATI T5, 6 x 24 watt fixture.
Approx. a month ago I was thinking that the T5 experiment wasn't getting growth like I wanted so I shopped around and picked up a used gen 1 Radion with the intention of sending it in to upgrade to gen 3. ( gen 3 color is soooo much better IMO).
About 2 weeks ago I was taking pictures and comparing growth and color from a couple months ago and it's then when I noticed almost everything had doubled in in size. Some even more.
Things had really taken off , but I was so focused on getting a Radion back over this tank that I wasn't really looking at it.
Just as a little color test, I took a small colony of rastas from this tank and moved it to the tank that has Radions over it and IMO, the color wasn't any better. And after a few days the polyps looked a little smaller.
Before I went to mostly all zoanthids in this tank I had all lps/sps with the Radion over it, and the tank thrived. The growth was amazing. Color was huge.
But for zoanthids, I'm leaning towards T5's.