I'm signed up for the 50k this year, looking forward to it. Another tough one is Speedgoat 50K here in UT at Snowbird - it has ~1k more vert than the Rut, but not sure how the terrain compares.
you'll "like" it
I had Speedgoat on my list, but never made it sadly (or maybe not sadly ). Another one on my list that was never completed was one my buddy had done, the Volcanic 50k- circumnavigates around Mt St Helens crossing a couple of major drainages, some rock scrambling, etc.. He said some of it looked like moonscape where the volcano blew, but other parts perfectly intact Pacific rainforest- lots of contrast in the 30+ miles.