The size of the house is not a direct input to the size of the furnace that is required. WIthout a heat load analysis, it is impossible to say what you need. It was not very uncommon to have builders just put a bigger furnace in that was actually required just to make sure. Energy wasn't too expensive back then, and people didn't really care. A smaller furnace might be more than enough. You know that the 100K job is big enough.
At the coldest temp, an ideally sized furnace is running constantly. You obtain the greatest comfort when it is on all the time, thus, no ups and downs in the indoor temperature.
A good heat load analysis requires knowing the size, quantity, and type of windows, doors; the quantity of insulation, and the anticipated temperatures, the length of the exterior walls plus probably a few other things.
Only when you get this done (and you can probably find a spreadsheet on-line that will help you calculate it) will you know how big of a furnace your house really needs.
Note, once the furnace can't maintain the set temperature (i.e., it is running all of the time), the house doesn't magically become a refrigerator - it drops a little with each degree the outside temp drops. Eventually, it reaches an equibrium - putting in as much heat as is leaking out. That is why is it required to analyze the house - leaking windows, insulation, etc. Once you know this, you can intelligently choose the best size for your conditions.