The easiest way is to shoot a wall with all 3 on. You'll see the beam patterns and how they mix.
Don't have it all yet ... I parted ways with my G9 setup in its entirety, intending to house my D700.
I've since been "backsliding" towards a G10 + FIX setup ... but haven't made a final decision.
As of yesterday, I was back on the D700 ... but then I start wanting the S&S with optical ports and the nice, affordable Ikelite option turns into a new car ...
You can bet whatever I do get that I'll shoot the "h" "e" double hockey sticks out of the wall and half the toy dinosaurs in my sons bedroom ... and then I'll move onto the YMCA pool ...
If I get the G10, I think I'm gonna try some kind of three strobe setup - either three s-2000s or twins with the old YS-15 in the middle. On night dives and macro-setups, I'd reserve the center slot for a focus light, but on w/a I think I'd like to give the third strobe a whirl.
I need to decide soon as I'm going to St. Croix in June.