The magnums are great, I'm running 4-8" magnums and 2-6". They have massive interior volume so they run real cool with proper sized fans. They definitely seem to spread the light a little more than your traditional yieldmaster or supersun.
I don't think the spread will be too much at all. Search over on grasscity I think there was a thread a few years ago where a dude compared about 10 reflectors on a 4x4 with a candepower meter. The magnum was new at the time but If I'm not mistaken it came out on top or damn near while running a good bit cooler. The supersun2 and and radiant were tested and generally known to be the 4x4 reflectors of choice previously.
Sun systems has a new reflector out called the Luxor I believe that is a vertical bulb arrangement, might be worth checking out as well.