Yes we've utilized both Post Title and the Google Keywords for the autocomplete.
I've gone through all details regarding optimizing performance and it still seems too slow. It takes a solid 5-6 seconds to display results and the autocomplete is too slow, you have to type very slow for it to be of any use.
We have about 850 posts in the WordPress database and are using the Index table, but still painfully slow in comparison to your demo's which are lightning quick.
Let me know if we can do anything to resolve this.