I’ve just got back from a tour of France, Spain, and Portugal. Followed a fair number of Eurovelo routes: Rhine to Rhône canal, EV6, 15, 8, 3, 1.
In France many of the old canal toepaths and tracks by the rivers have been asphalted and painted with dashed white lines (bit overkill if you ask me). However in Spain the pilgrims’ hiking routes have been included in the EV bike routes, but are really just old, stony goat paths, maybe fit for a mountain bike, but not much more than that.
I often had to use Google Maps ”car without highway” to avoid them.
Speed difference? 50 procent I reckon, but I’m on high inflated 32mm Hardshells. My sighs of relief when getting back to asphalt (or at least hardpacked gravel) must have seemed very strange to the goats and pilgrims.