Indeed. But perhaps we should address his doing three consecutive days of metric centuries. This is not that hard as long as you aren't riding hard. Rolling resistance of a CX bike, which is probably applicable if you are going to do the entire trip on dirt, is probably in the 30 watts area with 32 mm knobbies pumped to 70 psi. In general aerodynamic drag goes up pretty rapidly. At 12 mph you are generating perhaps 20 watts of drag and that doubles by 15 mph and that doubles again by 18 mph. So if you want to do three days of metrics you probably want to hold your speed between 15 and 17 mph.

Of the last two hard rides I've done, I've only averaged a little over 12 mph and a little over 11 mph. Two weeks ago I did a 50 miler and averaged a little over 15 mph. So that should give you a reference from someone that has about 1,500 miles in for the year. Hopefully that weather will improve and I'll be able to do longer rides.