The editor limits the speed value in the "Show Scrolling Text" command to between 1 and 8. This plugin will allow you to use any value above 0, including decimals, so your scrolling text can be as slow or as fast as you want.
It works by using a plugin command that overrides the speed for the next scrolling text command, ignoring whatever value is specified in the dialog. After that, any subsequent scrolling text command in your event goes back to the normal default behavior of using the dialog speed, so if you have more than one scrolling text command you want to modify the speed for, just use the plugin command before each one.
Version 1.01: The plugin command will no longer persist outside of the event page, just in case you left one floating around without a corresponding "Show Scrolling Text" command.