Casa to Marrakech ~3hrs. Fez to Casa ~3.5 hrs. Assuming good conditions. These roads are great.

You can probably plot a route from Marrakech to Fez that lets you see plenty of the mountains, potentially saving you the extra trip out from Marrakech.

Here is a post on Frommer's recommending a route. (See Uniall post)

Out in the boonies between Marrakech and Fez, you may encounter more trouble getting food, as there are fewer foreigners.