This will be my first time. I tried to get into Leadville this year, but no luck. I'd think races like LOTOJA are hard, but at least they are supported. Nutrition and hydration would be really hard with white rim.
I have done Mount Rose to Mr Toads Wild Ride in Tahoe, which is a big epic MTB ride with some technical downhills that you'd probably enjoy. These big rides are so hard, but so rewarding.