In Sudoku for Windows Phone 7, what is the maximum amount of XP possible in a single round?

This question is in reference to this particular version, the Sudoku that is available via Xbox Live on WP7. I'm on my way to the "Ultimate" achievement and want to know which gametype and combination of powerups will net the most XP in a single round.

I suspect that "Lightning" mode, combined with "XP Bonus" and "Gamble" will do the trick, but I want to know if there was something I was missing that would help get me the maximum amount of XP per round -- and also what that value would be.