I may be wrong but I seem to remember being told the XE airframes were actually Mk2s re-manufactured as Mk 3s by addition of the later wing; the Mk2 originally having a wing with parallel leading and trailing edges like the single seat Mk1.
I only flew Mk3s in the WT and XA series. Some of these had spoilers, and very effective they were too; my forte flying AEG cadets was to turn base leg at 300ft, and open the spoilers 'over the hedge' (you weren't supposed to go beyond the downwind boundary of the airfield in a Mk3) resulting in an almost vertical descent to spot land at the launch point, with the nose of the glider over the next available cable, one cadet out, next cadet in then off again. Great fun!!