Shout out to my current 2.25 Aspen's. Over 1500kms on dirt, including a 3hr race in Bendigo, 6hr race on Bright, multiple XCO races in Vic and general training miles. When I replace it I'll go with the exo casing as I've managed to get a few sidewall cuts, but nothing that's actually gone through and given me a flat, knock on wood.
Currently running a 2.25 Rekon on the front of the XC bike and it's a good tyre in-between the Aspen and Ardent race. Will keep running that up front this summer for the extra bite in the dry and dusty conditions. Only 400kms on it so far.