The performance are not the best in the game "Commodore Shawn" says that performance improvements need to be done with the game.
And map types are not, as much as i know, to change the size of the map. They only change the generation features. For example: Mesopotamia worlds generate with deserts and lakes instead of large oceans, Mediterranean generate ocean in the middle, a ring of land attach to the borders of the maps, and more rivers.