Premium vs. Regular gas in a 1998 Lincoln Continental?

I just received a 1998 Lincoln Continental as a gift. Has only 31,500 miles on it. I don't want to mess up a great present, but I also don't want to waste money. Most of my driving (95%) is within 5 miles of my home, all street driving (45 mph or lower). Some articles online (cartalk.com particularly) say that with this type of driving, 87 octane is fine, even if the owner's manual calls for 91. What has been other's experience?