[ubernostrum]

I don't know what's involved in Pre.

But GE involves CBP going through employment/address history as well as every time your passport's been used and any issues you've ever had at a border (I know because I heard a guy at the next desk being grilled in his interview about a piece of fruit in his luggage when I was in my interview). And NEXUS involves having both the US and Canada run checks on you independently.

So in terms of rigor, NEXUS > Global Entry > Pre seems to be the way it goes.