That depends very much on n, though. If Marquise gems continue to drop, you can only go up 3 or 4 grades, I think. That's 27 or 81 gems per socket, compared to 2187 now.

Anyway, if you're already a multi-billionaire (like I assume pichapie is), picking up 10-15m gold per downgraded socket is just a drop in the ocean. I'm not going to bother.