I got 2 Eheim 2215s and 2 200W Hydor inlines on my 75 and they seem to be doing the trick, I read that the heaters failed sometimes and I decided that I would keep 2 smaller ones on the tank so that if one got caught in the on position my tank wouldnt be fried. I haven't really noticed a reduced flow either, so there's that. As for going bigger with the canisters, I would. The flow is a huge limiting factor, it doesn't penetrate the surface well so a bunch of the biofilm is currently reigning supreme, but I'm going to get an aquaclear surface skimmer to fix that. Good luck!
