I say not much different to a chain -shockwise - when you got no original shock generator on the crank.
Also I see no need for worries on a Vincent with TWO chains on the bike, primary and secondary. So no real hard shocks on gears. Chains are told to be too soft for overhead cam drives, so there . . . . . Again, Guzzis and BMWs got not a single chain in their drive , all hard gears, just the known ESA in gearbox - and they don´t crunch their gears all the time - well, mostly. And their gears are a lot lighter than the heavy Vincent components. Has anybody ever seen pitted gears on a Vincent at less than half a million miles ?? Even after snapping a triplex chain - they do reportedly - nobody needs to scrap gears from this harsh incident.
Vic