I currently have two MP40 on my 80, one on each end panel. Before, I also had an MP10 on the back, it got loud (bad bearings) so I removed it and have been too lazy/cheap to replace it. Before that, I had two Tunze 6095. And finally, before that, I had three MP10, one on each end and one on the back.
You will get the best flow patterns using three pumps. If you are going with a mostly SPS tank with a crapload of rock, then you should use two MP40 with the MP10 on the back being optional, but it does fit best when using the Ecosmart modes (Nutrient Transport and Tidal Swell). If you have an open rockwork layout, then three MP10 would get the job done.
The only issue I have with the MP10 is that you need to run them higher than the MP40 to get good flow in the tank, and with that comes more heat, which kills the crap out of the bearings since the MP10 has no ventilation. They also will pull in air from the surface even if they are several inches below the water line, so they'll blow bubbles and make a slurpy sound.
The MP40s are great, and they bring a broad, oval shaped flow (whereas the MP10 has a round flow pattern, though still wide), but with that flow it can create whirlpools that push the sand around a bit if you don't use a larger grain. I use Nature's Ocean Samoa Pink 'gravel' # 2, which ranges from 0.8mm to 1.5mm, and it does get blown around. I've been thinking of capping it with a layer of gravel #5, which is 1.5-2mm and would hopefully not be blown around, but knowing my luck it won't help at all lol.
