I drive the XS but haven't driven the RE-11 so I'm relying on the shootouts for comparison. GRM said the XS did not have the stiffest sidewall but overall design proved the "stiff sidewall" quality was not essential for performance. For GRM, XS outperformed RE-11 in aggressive driving. Designing past heavy sidewalls also made the XS lighter in weight.
Some of the Tire Rack drivers got their best times with the XS. Luke said different driving styles may account for some drivers doing better with the XS.
In my own driving I felt XS was not quite as good on the wet as the MX I had before, but a lot more dry grip with XS.
This all seems to bear out the theory that XS is tops in dry grip but not a standout as a rain tire.
Driving XS is the 50's seemed fine for me. The tire warmed up after couple of minutes and had a lot more grip than anyone behind me.
With XS ratings so close to RE-11 in shootouts so far, price is a valid comparison.