Means it's as hard as a 8B straight up doesn't it?
Imho it is pretty pointless to compare.
A comparison with roped routes should be easier in many cases, especially for the aller-retour stuff.
A few first hand examples :
Long 7B-shake- long 7B gives you 7c/+ trav. (eclipse pensées cachées)
6C/+-shake-6C = 7b trav (Jules Verne)
Continuous stuff with no rests consistently feels one grade stiffer compared to a bolted route of similar pumpyness (7b+/c trav=soft 8a route, danse de printemps)