easternreefer, your Kessil makes serious shimmer. But mcgyvr is right, you will lose some shimmer... maybe even most of it except where the Kessil light is strongest, in the center of the tank.
Wagonpitt, I'm far less sure about your situation since you are kind of guessing at what led puck you might use.
I have a Reef Breeders Photon V2 50" led and I have pretty good shimmer because I have really good surface agitation and my leds are 12" off the water. I added a Sun Blaster Nano 48" t5 single bulb and that cut my shimmer by about 50%. It also made my corals look more pastel rather than the bright, higher contrast color I get with just the leds. I know t5's are supposed to improve leds as far as coral growth and color go. But I'm not buying it. My corals grow well enough with just leds. After all, I'm not raising a cash crop in my tank. And maybe the color improves over time, but I like my crisp, cool white light with corals that fluoresce and pop. So I'll stick with my leds.
In fact my t5 fixture now has a Bio Tek 20,000k & UV retro fit led bulb so I can still use it along the back glass to light the corals that I have growing off the back glass about 2/3rds of the way up the tank. The Photon V2 struggled to light them well. So now the t5 sits on the back euro brace and screen at the very back edge and now those back corals really pop too!
