Interesting thread. As a beginner bikepacker who rides gravel, I can offer the following.
I rode my gravel bike fully loaded for the first time this weekend, just to see how it felt with all the gear. The statement below sums up the experience well...
You will see how more bike+load weight completely changes what you considered adequate gearing before.
The bike has a 34 ring in the front and a 36 sprocket in the rear - about 26 gear inches. It did OK in the north Georgia peidmont but it was lots of work. A lower gear is going to be needed for real mountains.
Looking at Absolute Black 46/30 chainrings but a bike from Rodeo Adventure Labs is starting to look better and better, or something capable of true mountain bike gearing.
-Tim-