There's a few things I can try.  Though I'm not seeing much slowdown from my end.  I can see some really slow queries in the logs, but there aren't many of them.

Bots no longer seem to be that much of a problem now.

(29/05/2014 02:13 PM)Joom Wrote:  What I don't understand is what's making them target this place so much. There are much larger forums that contain the same content. Is it the MyBB version or what?

I doubt bots care about the size of the forum.  It's usually related to how easily they find it.  I find that inbound links seem to help them find forums to target; that or just a regular web search.