as100P comes with the pump so u dun need to worry about whether u can use yr eheim
i also jus converted from 2012 to as100P today and volks, it can be hang on, trust me cos i jus bought it todae
as for the macro as350P i've been using on my 5footer, i'm very sure i didn't buy the wrong skimmer, it can skim out alot in 3 days during the starting phase of my tank when i had only 2 tangs.
during the same period, in comparision, my weipro 2012 (which serves my 10fish fowlr) skims out less in 1 week than wat the 350 (which serves only 2 fishes) skims out in 3 days