I have a 58 gallon oceanic reef, mixed with quite a few SPS. Not sure what size vortech to get. Is the mp40 overkill, is the mp10 under par and what about looking for used mp20. Any thoghts would be nice.
A used mp20 would be nice for you. A mp40 turned down would be good, especially if you upgrade in the future, and a mp10 would work, and you could always put a hydor behind your rock work for extra.
I have a 46 bow. Mp10es. Short pulse 3/4 turned up. And a hydor evo 750 behind my rock...
I have a mp20 and mp10 on either ends of my 75 gallon tank. I think 2 10s would be perfect for you, 1 would even do the trick for a while. To be honest the 10s really kick butt, I get way more surface turbulence on the 10 side than the 20. They both are worth it, but the 10s newer technology with better programming. Go with what you can afford Id say.
I run one New MP10 on my 65. Which is almost the same exact size of your tank. It does the job, but I also believe the coral placement and rock work affect the performance of any powerhead. I also run a Koralia 2 on the opposite side but it faces the front of the tank to get flow going along the lower part of the tank.
I can only speak for the mp40 and I'm running it in my 65g. It's been working well for my corals thus far. But like others have mentioned, rock work is a big factor. I have the mp40 on the right wall and it's not enough to keep all the detritus suspended - even at full blast. Note that I do have a decent amount of rock in the tank. Stuff pools up below the Vortech and I rely on another pump (on oscillating schedule) to blow it back up into the water column.
I personally do not think it's overkill at all. Price wise maybe, but not performance.