Question: Is there a specific forum related to website performance here on SitePoint? If so, where? If not, why?
Server ManagementDiscuss server hardware, software, processes, installation and security for your dedicated server, VPS hosting and cloud hosting here. Both for *nix as well as Windows based servers.
No! Website performance as in: Why is my site slow, how do I get it to load faster? Basically a forum to talk about site performance on the client side.
That would fall under Design Your Site - SitePoint Forums
So the "Web Page Design" forum would be the correct spot for these issues.
I probably agree it were just 'client-side' issues then "Design Your Site" might be apt - but usually a server is also involved. Even if you post the question in the wrong place; myself or another Mentor typically request a 'post move', etc.