You should really go check out the other Leadville threads where this has been discussed. Like, this one for example, and then then read through the yearly threads below. But, 2.5 w/kg NP at altitude is around 9 hr.
This year I was NP 196, Avg Power 156, VI 1.26, 80 kg +/-. Sea Level W/Kg right around 4.0 +/- depending on the day. NP W/KG for the race 2.45. Time was 9:02:28 on a pretty good day. I could have gone sub 9 if I’d had support and been in/out of the aid stations faster, or just pushed a little harder because I had a little left in the tank meaning I could have pushed harder up Powerline, although I’m splitting hairs. Had a really good day overall and was trying not to blow myself up.
Check out these threads too, there’s been a LOT of discussion on this race in the past.