I'm replacing a 9-speed cassette and the shifter, but keeping the RD. I wonder if the RD (Shimano Deore XT) would be compatible with a 10-speed drive train. My understanding is that the pull ratio is 1.7 on both so it should work. If that's the case, I might as well go with a 10 speed system since there seems to be more choices out there.

Thanks.