What technology would you recommend?
I have changed hosting. It is now possible to use Memcache or Redis and OpenLiteSpeed or PHP-FPM. What do you recommend?
My recommendation would be stick to Nginx + PHP-FPM + Redis + A caching plugin at first and see how it performs. Nginx is quite fast any way. And in any case you should exclude the forum page from your cache plugin, here is the instruction: