I have to agree with harrowing, the differences between the 300 and 400 are significant, and the most important ones such as engine operation, recall items and aircraft limitations are the ones you need to know instantly in an emergency. So if you're going to get it wrong, it won't be a 2kt overspeed on descent, it will be something a whole lot worse, probably a lot closer to the ground.
Why not just make Melb/Mildura Q400 only bases?
And how about we put this back in RPT - seriously who thinks Qlink is a GA operation? (no jokes please) Do you have to have a jet to get in the RPT forum?