Unfortunately, for those of us without 7 League Boots (which is probably pretty much everyone in the world apart from you) normal walking pace is about 3mph (or 5km per hour). If you're travelling from one village to the next, that's the maximum speed you should allow for.
(There's a point where it costs less energy to start running than to keep walking - that's about 4mph, or 6.5km per hour. Next time you're on a treadmill, walk for an hour on that speed setting. Then do an hour at 5mph. Then imagine spending a day walking at that pace.)
3 to 4 mph depends mostly on height/length of stride. I’m just shy of 6ft and I have walked 4mph for around an hour on a treadmill many times. That’s how I came back from the edge of the worst obesity I’ve ever experienced. Well, that and the standing bike, which I’m not sure the speed of because I just put it on the “variable terrain” setting and then watched some DC CW show episode. Either way, I did the walking hour at least once a week for several months. I also walked my dog at around 3.5mph average (the dog gets distracted) regularly for the first year and half we had him, because we are in a small apartment and he had too much energy to not do so.
Perhaps our definitions of “comfortably” are different. For me, it just means it isn’t painful and doesn’t leave me wrecked after an hour or so. If I can do it for even half a workday, or 4ish hours, without significant pain (sometimes just being conscious hurts) or being too depleted to do it again after a short break, then it’s comfortable.
Others seem to use the term to mean “without any particular extra effort”. In which case, sure, 3mph, give or take a bit for length of stride and general energy and fitness.
If I’m pushing myself, I could do 5mph without pain for quite a while, as long as I had food and water before, and snacks during, when I was younger. If “comfortably” and “pushing yourself” are incompatible by your definition, then feel free to translate that accordingly I guess, I’m not going to try to get you to change your definition of a word.
I used to often walked 6-7 miles to hang out with my friends when I was younger, since I didn’t get a car until 25. It would take about 2 hours sometimes 2 1/2, which includes time spent waiting for lights, slowing down bc I got a phone call, etc. My average speed was around 4mph, in decent weather, but that’s average, meaning I walked faster than that for a good chunk of the time.
The key point is you aren’t walking the average speed the whole time. You’re walking slower at times and faster at other times.
I definitely know people who can walk faster than I can, though most of them wear out faster as well.