First, if the Donner party had 145 hp, they would have killed themselves because they rode a GSX-R through a snowy forest with no roads.
Second, the power loss on my bike was slight. I normally live at 6000 ft, and most of my riding is from 6000ft-9000ft (I love Colorado!). Even at 12,000, I could easily go as fast as the rainy, freezing, almost-snowing conditions would make me want to go.
And if you choose a unique, less-travelled path through the mountains, you'll never come across more than one motor-home at a time. And even with 35 hp, I could still get up enough speed to safely pass them.