Great point on the rear gearing. I am running a 10-50 rear cassette.
In terms of gearing for Leadville, Powerline is just SO hard. Even a 28 would feel like not enough, and that’s coming from somebody who rode Powerline in reportedly the best condition it has ever been.
I think a 10-52 or 10-51 could be good for Leadville. I was in my 50 for the steep part of columbine where it turns to a Jeep Trail, and all of Powerline, but other than that, I bet the vast majority of my day in terms of time was spent in my smallest 4 cogs.
Another thing to consider is clearance of frame and obstacles. Assuming your frame can clear it and that’s no issue, if you are on a rocky course, a bigger chainring could mean you smash a rock or log when you otherwise wouldn’t. On my SB130 I have a OneUp chainguide / bashguard combo that works well with a 34t, but I’ve heard of pro enduro racers judging their chainring size entirely off of whether or not they need a bit more clearance to not smash their bashguard and lose momentum in a critical section.