I am running an ASM G4-X(modded to be a re-circ style) on my 120gallon it does the job really good, still could be better though. When I upgrade for this tank it will be either Warner Marine K-2 or MSX 250, I may try the Vertex cone skimmers too, just not sure if that brand is still having pump issues.
I don't think the G4 will be enough either if stocking is heavy. Turbonegro has a Reeflo 250 on his 400+ gallon system. There really are many choices here, just make sure it will fit in your stand if that is how you are doing it, your not using a different location for the sump are you?
Matt