i quite like doing one arm stuff but pinching the door frame (if your board presumably is) with the other hand works pretty well and means its really easy to vary how much weight is being taken off
ok, so you 'may' finally have a use; given you do both, for the same grip type, what weight do you end up adding for both arms?
you will be able to dead hang a campus rung paul one armed for definite,( if you can't i would a. be flabbergasted and b. guess it would be shoulder weakness)
I would suggest Ned would be a good person to ask.)
to be honest all my fingerboarding is guess work!