I don't get either the scale for server load, but, have you noticed a significant difference with a without the mod ?
Where you using the no dupe (it's the one adding a left join on forum index, but can be deactivated in acp) ?
As well, with a Arabic (or is it Persian) language, the advanced mod rewrite isn't necessarily a wise choice, if your topic title never uses Latin characters, the mixed is enough (and the simple is if your forum do not use Latin chars either).
Another thing to keep in mind is that our SEO mod do work, and if you started to use it with the zero dupe on, it's rather normal that you first experienced more load on the server, because bots at first do crawl the link they know already like crazy (lasts few days when the redirecting starts) like if they wanted to be sure about the redirections, then it goes back to normal.
And then, you'll have more visitors so, the server will have more work too for theses reason which are not related to how fast our mod are (they are!).
So all your measurement do not mean much if you do not provide with data about visitors, did you have more visit, more page loads than usual when experiencing the over load is a real good question to answer
