Flight Safety--
I would recommend that you have dedicated crews for each type. IMHO mixing two completely different types (as in your example) does not promote safety of operations. This was tried many years ago in a large corporation that I worked for, and NONE of the crews liked it. In fact, come to think of it, we had three types, B727, GII and FH227. Guess which type generated the most flight hours and actually PAID for itself? Yes, it was the FH227, based in Teheran. We averaged 145 hours per month with two Captains and one (rated) First Officer, six days per week. Was much younger then so the pace was not noticed.