In 1997 I had a Trane two-stage heating system installed and am satisfied
with it. It replaced an oversized less efficient furnace, so I can't make
an energy comparison. Before, I was being blasted with gusts of heat
followed by cold periods. The thermostat could have been a contributing
factor. The new system has an "intelligent" timed thermostat. When it's
set for 60 overnight and 68 at 6:00 am, it will start warming the house
slowly at about 4:00, resulting in much more even heating. You may want to
place more emphasis on a good thermostat than a fancier furnace.