I used Shimano MegaRange(freewheel on the LeTour, Cassette on the Prelude). I like them because you get a fairly tight set of cogs and then a big jump to the 34 tooth bailout cog. The freewheel jumps from 24t to 34t and the cassette jumps from 26t to 34t. This gives a nice set of ratios with even jumps using a crossover shift sequence and then gives your bailout gear when things get really tough. I'm using a Shimano Deore XT model 750 rear derailleur on both bikes.