I am late to this thread but 2000 from 68/4500 sounds pretty good, maybe a bit high. However it took a while for me to find a reg that can go low and stay hi-flo. I finally got the DYE gen2 inline reg.
It is working really well, but with just a bit more tweaking I think I can get a bit over 2200 shots with my 88/4500.
Book of Linuss Chapter 1 verse 4 "If it has to be explained then it's not for you"