I have a RSM250 as well, that I bought used from a friend. He had it set up with the lifereef nano siphon overflow. I can get about 240gph pretty silently with it.
http://www.lifereef.com/siphon.html has some pictures of that particular style of overflow.
I have a 40g sump in the basement under the tank, run with 3/4" flex pipe and then some lock line to get it in the tank, replacing the stock power head on the left side of the tank (I have the hole in the back wall plugged with a rubber stopper)
It's totally worth it for the extra space for equipment. I have a 40g diy sump with a refugium for chaeto that seems to be using all the nitrates before I get algae in the RSM, and room for all my extra LR, and a skimmer, plus, basement water changes are easier.
The space in the back of the tank is kinda wasted, but I built a pod hotel out of some corrugated plastic but who knows if that does anything.