I actually have a 45G tall myself, and bought the Octopus BH-300F at reefwarehouse.com on sale, and I haven't looked back. It has a HUGE footprint that when put in the exact middle of the tank, takes up a bit but honestly it's much better than my prizm, plus it's rated for I believe like 90G.
It started out VERY noisy, but has quieted down quite a lot....my return pump is louder than it.
Hope any of this helps!
Josh
PS. Just checked......they put it on sale again, it's $175 and includes free shipping