We host 3 GiB of downloads, which increases with every release of course.
The only solution is to use a service that's redundant. As long as we have a single root server for serving the web services, adding mirrors won't do anything. Of course we could use DNS round-robin, but that's more of a joke IMO.
Using "good ol'" and capable webspace (read: managed) would solve the issue. GitHub pages is not good enough, we need PHP-enabled webspace for the forum. It doesn't make sense to split services for the main site and forum, when you can get one that handles both.