I think he meant what Shimano specs rather than what is possible, though it's only correct for 11 speed. Prior to 11 speed there was no difference in max cog for SS or GS. In actual practice, I've also used the 30t on 6600, 6700, 6700A, 7800 and 7900. On one bike the 7900 works but the 7800 does not. Just have to try.