Metats, Sapho Juice and mixing with Spice

Okay, it’s been awhile since i last played Dune, though I plan on having another campaign next year, but from what I remember none of the classes had been thoroughly explored on the core book. Mentats, as an examples, have Juice of Sapho mentioned on their introductory page, but this juice isn’t an asset thay can be used by the players. And just now I was wondering what would happen if a mentat used both Sapho Juice and Spice at the same time? Would their minds rival those of The Great Old Ones?