I still have good clearance as I maintain a .675 tenon.I don't think it affects the threads at all as I understand it the insert is only as long as the barrel and the pin is threaded into wood below that. Which makes threading the insert unnecessary because it's not bearing any load. It's only purpose is to keep the pin dead nuts while gluing the pin in. It is in no danger of falling out with the cue completed simply glued on the outside to the inside of the core. Threading it would compromise the core by cutting toward the collar.
I find 5/8 tenon too thin and collars too thick .
.675 is the sweet spot imo.