I run Sram X9 mid cage rear derailleurs on both my bikes for the sole purpuse of having a touch more ground clearance to the lower jockey wheel. Both bikes have standard shimano tripple chainrings on the front, however the hardtail has 12-28t cassette and the dually 11-32t cassette on the rear.
On the hardtail I have full range of gear combinations, and the dually all but the biggest chainring and 32t cassette combo - but why would you want to run this combo anyway?