OpenStreetMap

Surface =compacted implies good surface even for road bikes, and wiki has "Best sort of ways below paving with asphalt, concrete, paving stones." This track is hard going even on a hybrid bike, with sections consisting of flints, cobbles, or just dirt. Suggest surface=pebblestone for large parts.
Some parts are tracktype=grade4 rather than grade3 (Even mixture of hard and soft materials).
The bridleway between Freshwater Co-Op and Yarmouth station is probably a good local example of compacted surface, although that is grade2.