The comp maps are not similar at all. The 52T wheel makes it to 47 lb/min (on the max efficiency line) at a PR of 3.0. The 56T is on max efficiency line at the same mass flow at a PR of 3.75. ie, the 56T likes high boost to make the flow.
If you have an engine that needs the boost to make the flow, then the 56T will be more efficient and further from the surge line. If you have a bigger (flowing) engine that doesn't need to run so much boost, then the 52T will suit better.