Regarding what williem said. Is the tread on the mondials more/less aggresive as the XRs? The XRs have been discontinued, and the mondials along with a couple of others are set to replace them, but the Schwalbe range is a bit confusing.
The XRs are bombproof and last forever in anycase. I would not like to say how much milage I have done on the set I have, but pretty sure it's over 10k miles and might be as much as double that. Several sets of speedo batteries worth anyhow, which normally run out every 4-5k miles. I think someone crossing Africa north do south did about 12k on rough roads theirs before they wore through. I the rubber formulation is very hard, and therefore they also seem a bit slippy on the road in the wet too.
Now using them on my Wiltshire commute, which takes in road on the way in and farm tracks on the way back and they doing a great job still.
/edit - PS I am aware of the mildly satirical nature of the OPs conundrum, but couldn't resist nerding about XR tyres in anycase.