EC2 Private Instance runns slower than Public

I’ve been testing my private instance using an AWS c1.medium machine (Agent ami-c262d9ab) but the performance of the test is extremely slow compared to the Public tests. In some cases it even times out when running the test.

I’ve been testing IE9,Chrome,Firefox. Chrome and Firefox runs the slowest.

Is there a way to check that the Agents are set up correctly or if I’m installing the instance correctly?

There is an installation check list at