It's actually a 125 gallon. The Eheim itself wouldn't provide enough turnover in the tank for that much capacity. I mainly use the HOBs as bio filtration and surface agitation and leave the Eheim as mostly mechanical. With the two Emps I have 4 decent sized biowheels and I think they lend themselves well to being a piece of the puzzle. Obviously I wouldn't use them as my only biofiltration, but in addition to some ceramic rings in the Emps and one of the baskets in the Eheim, I feel my bio-filtration is very strong. I haven't measured even the slightest bit of ammonia or nitrite since the cycle completed. We'll see how it keeps up as I increase the bio load though. I plan on fairly heavily stocking the tank as long as the filtration can keep up (and I stay committed enough to do the necessary water changes to keep the nitrate down).
The power head is helpful for keeping extra movement in the water to keep the sand clean for one. That and the black neon's in particular like to swim in the current. Tetras aren't known for loving too high of a current, but with the size of the tank the power head on one end and the Eheim spray bar on the other give enough to keep the doo-doo from piling up in the sand, but still leave enough calm areas for them to be fine. The power head is on the timer with my lights too, so at night the currents are down for sleeping.
Right now I'm in an apartment, so I'm not doing too permanent of a set up to want super long lasting fish. That and I wanted to build schools this time rather than a handful of larger fish. I've got a ways to go before I get some good schools going, but I bought out all the cardinals for now. My pleco is my only long term resident at the moment. A discus tank would be pretty cool. I've considered doing one myself some day.