The XR has a harder, heavier rubber compound that gives better durability and puncture resistance compared to the Supreme. It's tread isn't particularly aggressive so IMHO there is very little rolling resistance penalty. But this is moot anyway. Schwalbe has discontinued the XR and is only supplying out of a dwindling inventory. There is no better touring tire for mixed conditions. I stocked up with a three year supply of 37-622's and 50-622's.

The Supreme has a softer ride, has better wet grip, and is lighter than the XR. If you want some tread, especially for touring on rough surfaces, Schwalbe recommends the Dureme, which along with the Extreme varies only from the Supreme in its tread pattern.