Thanks for the suggestions - I have been looking at the USH for a long time. Looks like a good option - I wish I could go for the MSO - I have 35mm schwalbe sammy slicks on now and it barely fits on the back. I think the most I can go up to is 38mm. Might be interesting to put an MSO on the front and an USH on the back. Too many decisions - I just don't want to pick the wrong tire and deal with it for 8 hours during the race.

As for running tubeless - I want to go tubeless and carry a tube for emergencies. I run tubeless now and have gone below 30 psi with no issues. The crusher race has an extremely rough downhill section with washboards and I would like to be as comfy as possible and keep as much traction as I can.