Two MP10wES or One MP40wES?

I would go with an mp40wes and a mp10wes. Reason why i say this is cause its better to have a balance on the other side of the aquarium. Also you can run nutrient export mode and get more crap taken out by having another pump on the other end. I run this set up on my 75 and would also choose this set up on 55. Another member has already mentioned what I was thinking when he said you might discover 75 is better than 55 because of tank width. Much easier to scape unless you like rocks up against the glass.

Another thing to think about is if you only have one mp40 some of the detritus will be blown to the other side of the tank and not ever get removed unless you siphon out manually or something eats it. Personally I dont want to have to rely on tank mates to clean. If they help I think of them as more of a nice to have.

 

I am fairly certain an mp40 would be overkill for that sized aquarium and you would have to dial it way back anyway. Max glass thickness for an mp10 is 3/8" pretty much up to a 90 gallon aquarium.