I hike a lot in the White Mountains of New Hampshire, and around here our 'book time' is based off of a book called the White Mountain Guide. It assumes that you will take half an hour for each horizontal mile and each 1,000 feet of elevation gain, so a 10 mile, 3,000 foot hike would take 6:30 by book time.
This number can be useful for planning purposes, but it should never be taken literally; I'm far from the fastest hiker around, but on a good day and a decent trail I could beat book time by 30%, and of course there are many who could go much quicker. On the other hand, someone not in great shape or taking things slow could easily take longer than the book predicts. So personal ability is a huge variable in that regard.
Terrain also matters considerably- on a fairly flat trail, 3 mph is a reasonable speed (50% faster than predicted!). On a particularly steep or rocky trail, you slow down considerably. There are instances where taking a longer trail with the same elevation gain will actually be faster because of the ease of navigating. Even with the fairly constrained context of trails in this one region, the variance is huge.
And then we get to weather. Rain can definitely impede progress, but snow is the big kicker- if you end up postholing through thigh-deep snow, your speed could be well below 1 mph. On the other hand, if you have good traction and you're on a solid-packed trail, you can go faster than in the warm season (especially going downhill).
Basically what I'm saying is that there are way too many variables to give you a reasonable estimate. If you set Scott Jurek (recent AT record-setter) down in Kansas on a nice day, he could probably do 60+ miles and feel good about it. Put some average person in that same area in a whiteout snowstorm and they'd probably struggle to make it from their front porch to the mailbox. There's just no way to make an estimate with massively narrowing the scope of your question.