All the servers have basically the same configuration. Since this is a shared hosting environment, the speed is often affected by server load which caused by what everyone is doing on the server. Server load is usually temporary and resolves itself very quickly.
On the contrary, every server is running as fast as we've seen them in a very long time. They are running very fast, no high load. Load is under 2 on every server. Maybe your site is causing the problem. Have you checked for any poorly coded scripts?