I could see going 3 ways.
1) A pair of 6040's the advantage here is they are very discrete and would be place low behind rock work and be almost unnoticeable.
2) A pair of 6055's slightly stronger and easier to aim.
3) A single 6095's a second could be added for a more SPS intensive tank.
Normally I don't like single pump set ups, the redundancy of a second pump and the ability to alternate flow direction make dual pumps a better choice. However, a 6095 would cover the whole tank well and a cheap back up for emergencies would take care of any repair/ maintenance down time.