It is good to see there are performance braking options for the XJ rears.

I've been corresponding with EBC this week regarding their product offerings for the Jag IRS and keeping the rear brakes the coolest.

From their catalog (http://ebcbrakes.com/catalogs/), I came down to:
Rotors - GD239 (cross drilled & slotted) or USR239 (sport slotted)
Pads - Red (ceremic) DP3101c or Yellow (Ultra high friction) DP4101R

They recommended either the Red or Yellow pads and their dimpled & cross drilled rotors (GD239) for keeping the brakes the coolest.  Here is a pic to the part on Summit:
http://www.summitracing.com/parts/ebc-gd239/overview/

Here is their email back to me:
Based on what you’ve told me I would lean more towards the YellowStuff pads due to the fact that you will occasionally be using this car on the track. RedStuff pads are great for fast performance street driving but don’t have the 1200F+ degrees of heat fade resistance that the Yellow’s do. But If you don’t feel you need the extremely high heat fade resistance, go with the Reds. Both compounds will have similar heat dissipation and similar average friction ratings .48Mu friction for Reds and .50Mu friction for Yellows so your best bet for cooling is going to be the use of the GD rotors with either combination of pads.