You raise an interesting question for which there is likely no definitive answer. Interestingly, we cannot even be certain of exactly what Lincoln said, let alone which words were emphasized. There were 4 different news reporters taking down the speech verbatim, or at least attempting to do so. No two of them are precisely the same. The reporter for the Associated Press, Joseph Gilbert, was allowed to look at Lincoln's delivery copy, and thus, some consider his report to be the most "authentic". The really unfortunate thing is that many believe that the delivery copy has not survived. I say it is unfortunate, because it may have answered your question. Lincoln at times was known to underline on his delivery copy certain words that he intended to emphasize.