I think this is the wrong question. No one but SDA's say that the Lord's Day is Saturday. The issue on which there is debate is when the Sabbath is. Some Protestants will say Saturday, and distinguish the Lord's Day from the Sabbath. Others say that the Lord's Day is a Christian Sabbath, and thus apply the Sabbath rules to Sunday (possibly in some Christian adaptation).
Even the Reformed tradition is split on this. Calvin said the Sabbath is Saturday, and the Lord's Day is a free celebration. The Westminster Confession calls the Lord's Day the Christian Sabbath, and the churches that follow it tend to apply Sabbath rules to the Lord's Day. Even my own pastor, who normally follows Calvin more than Westminster, speaks of Sunday as the Sabbath. Personally, I don't consider the Lord's Day to be the Sabbath. (I also don't think we absolutely have to worship on Sunday.)