Either will do exactly what you want but in a different way. The Radion isn't any more powerful than the Kessil if you mount them consistent with their design. Radions are lifted high off the water to get a better spread. The Kessils have a far better spread naturally and are mounted much closer to the water (5-6"). In this configuration, they will produce almost identical PAR levels. So the question really becomes, what is your preference?
Having owned kessils and now Radions the actual spread of the Radions is superior if we are talking about spread, also like others mentioned if you have a plan and is not SPS heavy then either light will be more than enough and don’t need the pro version of the Radions, I have 2 XR30 non pro on standard 75g wish I would’ve went with 3 XR15 instead since I hace the option of spreading them to my liking. I wasn’t a fan of the cone look I got from my kessils A360w which were then older model can’t speak on the new ones, I currently have a A160 in my sump for my frags love both lights, Kessil definitely does a better job at blending the lights. In regards to spillage I believe all lights will spill unless you have a hood or Set them closer to the water line but doing so will loose some of the spread and Radions pack a punch and unless you have a PAR reader wouldn’t recommend it, 2-3 inches heigher or lower makes a big difference in pars