This is a new build in a community with one builder. They have set everything as far as the HVAC system goes. I am just curious if it is possible to upgrade to the XR17 vs the XR16 if that is worth it or should I just leave it as is.

I will defer to A Air,post your kwh cost before he arrives so he can give you a more meaningful answer.

It's through Pedernales Coop, they have a varying rate scheduled depending on time of day, but looks like an avg $/kwh is about .06

My last name is Austin, I don't serve Austin, Tx area. Yeah confusing right? I serve Katy, Texas area. If I lived in Austin, people would think I was royalty or something. LOL.

The Texas hill country tends to be drier. However, if zoning a system it's always better to go with multi stage equipment. Doesn't mean you can't do it with single speed but performance is much better with 2 speed.

If the furnace you are matching to a 2 speed condenser is not variable speed it will not achieve rated efficiency and in some cases may not work properly or take away from options that the system was ultimately designed for such as better dehumidification features.

So the XT80 with a four speed blower doesn't count as a variable speed? Are there furnaces with just single speed blowers? I know four speed doesn't count as a true variable speed.

There is a difference between variable speed and VARIOUS speeds. The first changes the speed of the blower while in use. The second has VARIOUS settings that the installer can choose between based on the BTU size of the furnace/AC.\

Normally, I would say that with a 2-story large house it would be better to have two systems rather than one. But since you're stuck with one, and two zones, you should get a multistage AC (and heat maybe) with variable blower. You'll be happier.

I've since found out that our furnace, the XT80, has already been installed. They are going to talk with the builder tomorrow about changing out with the XV80 and upgrading the unit to the XR17. If they are unwilling/unable to change out the XT80, any thoughts on the performance of the XR17 paired with the XT80?

The XR17 paired with the XT80 will not achieve rated efficiency of the XR17.

Exactly what the efficiency would be probably isn't known because AHRI doesn't test them like this.

It would be like going to car dealership buying a Camaro SS and putting a 4 cylinder chevy cruse engine in it. It looks fine until you mash the gas.

A system... any system.. is only as good as the sum of it's parts.