I have a a small (980 sq ft) one story house on a slab, in Michigan. I also have a small budget, and a house that isn't worth much. I am replacing a furnace that is at least 40 years old. My contractor has given me two quotes that are within my price range, one for an 80% efficient, two-stage, variable speed furnace, and one for a 95% efficient single-stage furnace. Aside from the gas savings with the 95% furnace, how do these options compare in terms of comfort, quiet, repair expense? Any other considerations?