As others have already pointed out, there's so many factors at play it's virtually impossible to make a determination without a lot more information. I do hiking as a recreation activity, where it has been starkly demonstrated time and time again just how much this can vary.
The biggest factors are going to be terrain, load, climate and weather, and each of these alone can vastly affect your travel speed. Another thing to consider is the size of your group; once you get up to large groups the sheer size starts to really impact the speed you can travel at. A Roman Legion, for example, would march all day and cover only 8 miles, which seems ridiculous, but each individual soldier would only actually march for a couple of hours; the head of the column would be setting up the next night's camp before the end of the column had left the old one.
A final thing to consider is endurance. We can all cite remarkable examples ; like the Greek army's legendary march from Marathon to Athens (having fought a battle the day before!), but that doesn't mean an army can maintain that sort of pace for weeks on end.