You need to size using the max gpg of hardness in your city water system. You can find that in the company's Water Quality Report on their web site or by calling them. That assumes you haven't saved the one they must mail you each year.
The constant SFR (service flow rating) of a 32k (1.0 cuft ) is 9 gpm and just barely over 10 gpm for a 1.25 cuft. You will get terrible salt efficiency in either of those softeners.
You should click on the sizing link in my signature.