OP here, after reading through everything I was about to pull the trigger and buy the M9A4, but found a used CZ75 SP01 at a local pawnshop for $680.
It has a threaded barrel already and all original paperwork. Since there appears to be a few decent companies that can do slide cuts for Optics for it if I want them; I figured I'd give it a shot out first. The worst case is that I flip it for a few extra bucks if I end up not liking it.
Pic of the new acquisition.