Do these differences actually make a difference in gaming?

Solution
Good for you. You will not notice the minor clock differences in game. You can always manually enter your own clocks and voltage tweaks after you get your card installed.
not a single review i have seen whows any noteworthy difference between any of the cards. the gaming, gaming x and gaming z were all pretty much the same. you can oc yours to get the extra 1-2 fps the gaming z gets.

enjoy the card and sleep well knowing you got just as much of a beast as the next guy.