Personally I think that pretty well everything useful there was to be said regarding the topic was covered three years ago. However, although there's no earthly reason why singers shouldn't ignore pigeon holes and sing whatever they like (as I do), the OP asked a perfectly reasonable and interesting question, and the respondents have done no more than try to answer it according to their own precepts.

"Just sing the bloody song" is all very well, but if that's all that everyone wanted to do there would be no need for Mudcat.