So these are 12 hour travel estimates on a good flat road in good conditions?
That would lead to an average travel of 2.5 miles per hour (4,2 km/h) walking and with horses it would be 3.8 miles per hour (6 km/h)
I am using 3 miles per hour walking and 6 miles per hour on horses for long distance travel of an average low training human for little less then 8 hours a day with normal brakes, we are on similar values here. I would also argue that with good training this could easily increase by 1/3 for speed and also an increase for number of hours used for travel per day. Exhausting the day could increase the speed by 1/2, but that would call for vulnerability on the road, an injury risk and a 2 days of rest afterwards.
Here is the travel speed modification table that I use for my game
* No horse riding available, but you can led it on foot
Speed Penalty 0% 25% 50% 75% Heat: Cool Warm Hot Frying* Wind: Calm/breeze Windy Gale Storm* Terrain: Flat Rolling Hilly Mountain* Growth: Open Prairie Woody Forrest* Flow: Dry Slippery Ford Deep ford Drainage: Steppe Meadow Marsh Mire*
Roads will improve Terrain, Drainage and Growth modifiers, and bridges will improve Flow modifiers
Edit: Yes, the guides. it is always good to have a local guide to help you with the trails and tracks in the more difficult terrain. Without the guide you may probably get a lost a lot or find hard time finding your way. If there is a road than this i not needed, also it is only actually needed when the travel takes the adventurers in the Mier, the Deep ford, The Forrest or the Mountains. The Storm will also mislead you if you do not have local knowledge or some way to find our way and the Frying conditions are extremely hazardous if you run out of water. A good guide should be able to speed up some trips, but it depends upon his skill, local knowledge and perhaps a little luck.