asbury, a maxijet MP40o should be fine
fender, good luck with your rios. They typically are decent pumps, however when they do die they have been prone ot create more problems, so keep up on themand if they show any signs of deterioraion or possible failure get them out quick.
I do agree with placement, criss cross is a good pattern.
trippclark, yes we do figure in the sump as well. In a 55 like yours, I would have probably 3 hagen 201's instead of a 402, but you could keep the 402 and add 2 more 201's and you should be fine. IMO unless you are keeping ponies or something that needs low current, I like haveing ALOT personally. In your set up I would probably have 11 to 1300 gph or so.