Curiously this issue appears to have been resolved. I'm not sure if it was through a number of successive changes without testing each independently or if I wasn't thorough enough in restarting services each time. But XPM is working fine now.
I did however notice issues with the speed of XPM when using IE within my VM (acronym overload!). I later switched out to Chrome on my host OS and any (perceived?) issues went away.
Thankfully I can safely switch back to Chrome now that the v36 issue has been patched!