I'm running a Fluval 304 and 204 on my 75. The 204 has a current going across the back from left to right and the 304 is at the back right pointing towards the center of the tank.
People who use Emperors seem to like them a lot so you won't go wrong with one of those either.
I've got an emperor 280 on my 20 gallon at home and love it. Do you think I could get away with just adding the 280 or would I need to step up to the 400? Thanks.