Simulation felt pretty easy. I ran at a sustainable long-run heart rate with one quick stop to roll out a problem calf (Achilles was barking, and I know better than to wreck those during hill season) I ended up going through a full 4 1-quart bottles. It's 70 degrees in my basement. My shoes were like wet bricks at the end. So, 2 1/2 hours of slog followed by 20 sets of 10 step ups, alternating legs on my patio garden wall (18 inches or so). I thought my legs would be burning afterward, but they weren't. I'll throw a sack of birdseed in a backpack and try a couple more sets this week before I lay off for a taper.
I'll say one thing. I've done quite a few uphill slogs on that treadmill at 15%, and 11% feels half as difficult. Altitude will be the real wildcard, I guess.