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So unless your mesh is starting out as a triangulated one, you may have a doubling or so of polycount.

Actually this is wrong. You will get more faces, but tri-count stays the same, no matter if your mesh is quad or tri. Every mesh is made out of triangles, just most apps hide them because quads are easier to work with, but quads are still made out of 2 triangles. Thus converting mesh will not change anything