Not an Ameriflight guy, but have flown part 135 turboprops and currently 121 regional dude. The folks I have seen move on the quickest to legacy are 121 check airman. Not saying its not possible feom the other routes, just depends on who you know more and timing in my opinion. For stuff like ACMI I know folks that had left seat Part 135 turboprop time and no trouble going to Atlas etc