It comes down to whether Oda sees a difference between Monkey and Ape here, since the words great are used with both. Plus, if I understand correctly, there isn't even a distinction between Monkey and Ape in the first place. And Supreme sounds better than just great. As for the size, the first SKG literally was at least as big as the KKG used in Dressrosa. Arguably, the SKG was slightly larger, as Luffy's main body looks smaller as compared to the fist.
And the fist of the second Supreme move looked exactly as big as the Supreme Kong Gun he hit Dragon Kaido with. But then again, he might or might not pull out yet another King version of that, which would look like the humongous fist he used against Douglas Bullet.
SKG = CoC KKG.
SKKG = CoC larger KKG (like Super Saiyajin God Super Saiyajin).
Seems like he didn't invent that move yet though.