The GHz requirements are very misleading because they don't take IPC (i.e. performance per clock) into account. Basically, a 2GHz Skylake i5 is faster than a 2GHz Sandy Bridge i5 because the Skylake i5 can perform more instructions per cycle due to more sophisticated architecture. In other words, the stated GHz is totally useless as the generation isn't usually mentioned. Your best bet is to search for people who have tried that game on the MacBook and read their experience.
On software that has minimum requirements, do we look at standard GHz or Turboboost GHz?
I.e. If a game requires 2.2GHz would a MacBook with 1.2GHz with 2.9GHz Turbo boost, which GHz would apply?