I never tested on such large boards ... and I recommend to test with the next version (will be more optimized). Anyway when I start this mod was the first thing what I start thinking ... how is working with large board ...

But if is working with smfseo then will work with my version either. Anyway read post about Url's ... http://www.webmasterstalks.com/seo-4-smf/seo4smf-urls-t923.0.html ... to see why is low cpu usage than any other version
Regards