The only significant difference between running a test in a test list and running it from the Record tab is that running the Record tab uses default execution settings while the test list will use the test list settings that are always linked to the test list. As David already explained, the 'ExecutionDelay' setting, adds the specified delay between each command, slowing down the entire run significantly. This setting is designed to make the test list execution more reliable.
Another thing you can try is when executing the Test Lists to use 2 Test List properties which can help you to improve the performance - in Test List settings, Edit Settings, Web tab - KillBrowserProcessOnClose and RecycleBrowser. Try turing each of them on to see if this will help your execution - these options are to forcibly kill all browser processes when a test finishes and to reuse the browser window and not start a new browser for every test.
the Telerik team