Performance is tricky to measure. Right now the best measure of performance I've got is the "blunder index", but that's currently flagging a lot of stuff that I really don't consider to be true blunders - I think my top priority for the next few evenings is going to be iterating on the blunder-annotator, and that'll help me identify what issues in the actual gameplay code to focus on. And the blunder index isn't really defined in such a way that you can do arithmetic on it meaningfully :)