Not sure what the average savings is, but if you are trying to do a cost comparison, keep in mind that there might be rebates in your area for more efficient furnaces.
The manufacturers should have this data based on their particular system so ask the installer to share. If you are considering a variable speed furnace, then considering upgrading to a high efficiency one at the same time. This would be a 90% + efficiency furnace.
Honestly, I am not sure why there are single speed blowers on the market still. Since the heating and cooling load on the house changes throughout the day based on the position of the sun, the system should adapt to keep you more comfortable. Single speeds do not.
Image riding bike with one gear. That is what a single speed furnace is. A blower with one gear.