My motives for asking the original question has to do with the project/CD I am working on at present.
I am going to record a large proportion of a particular singers collected repertoise, and there are also going to be instrumental versions of the some of his other songs interleaving the unaccompanied vocals.
Because the source is one particular singer (who has been long dead and we have no examples of him singing) I was wondering how different the songs maybe in different keys. Even though I don't feel there is a difference when I sing them.

Tim Radford