I’m not sure about the sort of precise figures a performance/algorithm researcher would be looking for.
However, in terms of actual performance there is no difference. The WP database can take a beating and I’ve done plugins with dozens and dozens of filters and hooks and queries and they still run very very fast.
Furthermore, WP is not known for its speed. It’s a great CMS, but cutting-edge performance/speed is not its strength. So I think there’s no point in worrying about something as minor as post type length.