I used to run a 9-speed derailleur on my X-Caliber 29er, which had a 11-36 10-speed cassette, because no one made a low-normal 10 speed derailleur. Not sure if that's changed since then, but probably not. In any case, I had to get a Tiagra flat bar road shifter because the 10 speed mountain shifters used a different pull ratio. Didn't have any issues with the 9-speed derailleur and 11-36 cassette.