Fair, but I wouldn't waste an entire RPGs' worth of slot for a bestiary unless I was totally obsessed with a game!the OP didn't set that; for example, the PF Core is one slot, the Bestiary is a second...
I'm curious, as a keeper myself and owner of the Investigator Handbook as well, what do you find essential about the Investigator Handbook? I find it extremely unessential if you own the Keeper book. It's a nice cheaper resource to have during character creation, in my experience, but that's about the most use I've gotten out of it.4) Call of Cthulhu 7e (I'm cheating here, because I can't see running Cthulhu adventures without both the Keeper and Investigator Handbooks)

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.