Availability of Dynasys is a big one, and it only matters if your using Dynasys shifters, which SLX comes in both Dynasys and non Dynasys. If your not, go with Deore. It only weighs a little more, costs a little less, and lasts maybe 5 miles less then the SLX. Other than that, nothing really that I'm aware of. I'm running Deore myself.

PS: this is Deore and not Deore XT, correct?