You might want to participate in the "speed discussions" in the "How do I" forum.
A good configuration of mysql is essential for a fast .threads forum. If the db is slow, threads can't be fast either.
I'm running a large .threads board with about 980.000 posts and about 300 users online at peak times.
It mainly depends on your MySQL configuration. You can increase performance with tuning the search and a few other things.
Feel free to contact me, if you have any specific questions. I've tweaking and tuning for several .threads owners.
