If you've been to my web site or read any of my replies about the correct sizing of a softener, you know I don't agree with your assumptions.
You need to find out how exceeding the hardness (and daily gals used) you size and program for effects a softener and what you have to do about it to get the softener to work right afterwards. Same for exceeding the constant SFR of a softener.
You will get terrible salt efficiency if you go with a "24K" or a "32K". And add water efficiency if your hardness increases and your undersized softener has to regenerate like every 2-3 days.
Day timer controls do not have calendar override; and use about 50% more salt and water than a metered control valve would.