Although it is the norm to common-rate 757/767 pilots, Thomsonfly have been experimenting with dual-rating pilots at smaller bases between the 737 and 757. Where they have one 737 and one 757 (I think Cardiff was the example used), the savings from needing a smaller crew establishment versus the increased training and recurrent costs make it worthwhile. Wouldn't be surprised if more operators started to do this, and with Globespan's increasing number of bases and fleet now split between 737, 757 and 767, it might make sense for them.