You failed to mention the increase in maintenance cost over the life of a condensing furnace. That is what makes them 90%+ furnaces they condense the moisture out of the products of combustion thus releasing more heat to the house pre cubic foot of gas. There are pros and cons to both systems, the high efficiency will cost less ove the long run but the temperature of the air leaving the vents is a little lower than the 80% units. So you will have to make the choice. A good 90% furnace installed properly will beet any 80% hands down.