I would also go with the 600 model, much smaller footprint in your tank. If you don't mind losing the extra space in the tank though, the 1200 is a better option IF you can live with that one drawback. You get more surface skimming with the 1200 and less chance of a clog/overflow problem.
Nothing is ever guaranteed when draining water from one tank to another. Even drilled tanks aren't bulletproof. That said, I would definately choose the Lifereef overflow box over any other. Worth the extra $. I started out cheap and had a few floods I didn't like, then tried a CPR and still had a flood when the aqualifter clogged.
So ya, Lifereef 600 w/ Mag7 would be a fantastic combination.