BRS has a nice video on them. They recommend 60% for one over a cube;
or 55% for two over a 4' tank. I had mine much higher: 2 G5's over a 60gal cube at about 75% if I recall correctly....(I've since gone back to halides!) :D
Definitely check out the above-referenced video. To answer your question, I am running a Radion G5 Blue over a Reefer XL 200 at 60% intensity with all color channels at 100%.