I run a 10 speed compact crank with an 11-34 cassette. I use a Shimano 9 speed mtn RD. Works fine and I know a half dozen other folks doing the same. My preferences for the RD are non-rapid rise and non-shadow. The LX T661 is kind of hard to find but may be a little nicer than a Deore or regular LX. Other option are older XT.