Though Embraer publishes a range of around 2000 miles, I don't think that the XR's "real life" performace will match that. Fill it up with full fuel and as many pax as you can throw on within weight limitations (or full pax and as much fuel as you can put on), and I think that at 2000 miles you will be flying a very heavy glider.
Houston to Palm Springs is going to be a stretch with a DP out of IAH to Dallas and then beating the winter winds to the coast. I think that dispatch and load planning are going to start earning their money when they start stretching out the XR's legs.
As for taking CAL's routes, if ExpressJet can do it more efficiently, then more power to them. At least for the time being, they are still on the same team.