Unfortunately the forum is causing my site to be slow again. Somehow it's not happy with the amount of topics that are migrated.

Could you please deactivate other plugins and test it? I just want make sure this time issue comes from wpForo. As far as i remember your website was very heave and it has lots of plugins.

After this test, deactivate wpForo, and test it with other plugins activated. This kind of test will help to understand where is the wrong point.

Yes I tried that. The website runs fine with all plugins enabled except for wpforo. If I enable most plugins and leave wpforo enabled it's still slow until I disable wpforo.

Ok, please wait for the next 1.2.1 version, it's deeply optimized and comes with  built-in caching system. We're planning to release it in a few days.

Ok thank you, I will wait for that.