What complicates things for biking is:

1) A major component of your effort, if not THE major component of your effort, is overcoming wind resistance. Wind resistance isn't as big of a deal with the slower speeds of touring, but a solid 20mph headwind will cash your check pretty quick.

2) The composition of the hills matter a bit. If the hills are close together, you can use the momentum from one hill to coast partway up the next hill, which makes things a lot easier than if you blow all your momentum at the base of one hill and start up the next hill cold.

I'd plan the ride so that I was riding with the prevailing winds at the end of the ride. Headwinds don't make such a difference in the hills (unless you're above treeline). You should do fine if you keep within your known limits, and you can recover in the second half of the ride if you get beat up in the first half.