Comparing trane Furnaces

I am building a house with the 2nd floor zoned off from the main floor/basement. The standard furnace is the Trane XR90. I can upgrade to Trane XL90 for $450. I know little about furnaces and was wondering what is the difference b/w these two and is it worth it to upgrade. Here are links to both. Thanks

http://www.trane.com/Residential/Products/Furnaces/XR90-Furnaces

http://www.trane.com/Residential/Products/Furnaces/XL90-Furnaces

One's a single stage burner, the other is a two-stage burner. The most comfortable heat is one that runs all the time. Since the winters aren't always super cold, for those mild days, the first stage is often enough to provide all the heat you need. Also, it's more efficient - same sized heat exchanger, but less heat going in means that it can extract more. The difference isn't all that much, but it's there...the bigger thing is the comfort level.