Cloudflare wouldn't help us with speed. We've tried them before, and they only caused headaches. Every ime we made a change to a css file for example, cloudflare would show the 'site offline' page for a good 5-10 minutes, amongst other issues. From what I can tell, the issue isn't slow database queries either. If you hit post and then half a second later, open the thread again in another tab, you'll see your post there, whilst the initial tab is still loading. Obviously IPB does a lot of additional processing after the post is submitted, and I have no idea what this processing entails, but it's clearly that which is causing the slow processing problem, and when we get time, we will look into that thoroughly.
I've noticed this several times, I usually hit "post" and it keeps "saving reply" for a good 2 minutes or more, BUT I can see my reply went through on the mini-spy. It's really annoying