Nice, I made something similar for version 6.3. Runs nicely for nearly a year now.
I UNION to combine the queries and it works well.
If it's faster or not depends on the number of posts and number of forums you have, aswell as on your mysql configuration.
Should be now problem to port that to 6.4, so I can post it here if someone is interested.
One thing you didn't mention is that a fulltext search only omitts words with less than four characters, which might be an issue for certain boards.
I already started to write up a new mod for 6.5 that has some more features and takes care of the new search caching. But I won't finish that one before the official release.
