I'm pretty convinced that if you were running Git Probes and not Preordains before the restriction, your deck was misbuilt. If you're running less than 4 Preordains right now, you should absolutely cut cards until you have them.
While I will most likely be trying a list with 4 Preordains to start, my philosophy before had been that casting Preordain equates to giving your opponent another turn. Number of Preordains is a matter of power versus consistency.
With Brainstorm it wasn't really like that because you could draw Jet, Ritual, Necro off of one Brainstorm.