We've investigated and solved the issue. As of the past 6 days the forum has seen an uptime of 100% and no slow page loads. We're terribly sorry that it took so long to solve this issue, but hope that everyone can now enjoy the again fast-loading forum :)
If anyone experiences any problems please don't hesitate to contact us (or post here). In addition to solving the issue, we've installed some monitoring tools that report the page responsiveness. This will help us detect similar issues more quickly in the future.