Eyeballing their game, I’d hazard a guess at 1500 strength otb.
M'Donnell's Double Gambit
Eyeballing their game, I’d hazard a guess at 1500 strength otb.
I don't think it's even remotely fair, or accurate, or insightful to try to assign an elo to past masters for a dozen reasons I haven't time to get into. I will say, with both M'Donnell and Labourdonnais I see a fighting spirit and resourcefulness often not exhibited by contemporary masters.
It isn’t denigrating them at all, in fact I am continually amazed at how good players back then could get with what must have been utterly abysmal training materials. I imagine most of their strength just came from playing lots of games.
In perusing the 1876 volume of the American Chess Journal (owned and edited by W. S. Hallock), I came across this interesting game, an example of M'Donnell's Double Gambit.
Here it is with slightly abridged notes:
Here is the M'Donnell-Labourdonnais game:
Here is the Mongredien-Morphy game:
Of particular interest to me is the variation suggested at move 5 in the first game's note: 5...Be7.
This leads to a variation in M'Donnell's Double Gambit called the "Four Pawns Gambit."
It goes like this:
Unfortunately, even though this is a named variation, I've been unable to locate a single example in any database.