Safari: shortcut to close one single tab without loading the webpage?
You could pinch to zoom out into the tabs overview view (or use the toolbar button for it), at which point you're presented with previews of every page as well as their respective X button.
Some of the pages will probably load while in this view, but generally not in a way that slows down your interaction with the tabs, which I assume is the important thing.
There is no function available to access the [X] when the tab is so short. You can only click the tab to expand it, or right click and select Close Tab.