What fuel is best?

I agree running uphill will definately heat soak the engine and so make it more likely to ping if there is too much timing at that rpm and load.
The only vehicle I've had that I recall having a different timing for high altitude is my '85 Grnd Wagoneer. Initial is advanced another 5 to 6* for high altitude.
So doesnt seem like knock was the concern - and that's on a vehicle where the owner's manual advises that high octane fuel may be needed.

That's why I'd try out the first few hundred miles on mid grade like 89 or 91 AKI. Then you'll have a better idea of what it can tolerate. If you can get 93 as you start into the long climbs, great. But if you use something less to evaluate with, you'll have a cushion when the going gets steep or only 91 or 92 is available.