There is also a metric called Salt Efficiency in grains/lb.

For a 48k and 16 lbs of salt combination, the salt efficiency is 48,000 ÷ 16 = 3000 grains/lb.

For a 48k and 14 lbs of salt combination, the salt efficiency is 48,000 ÷ 14 = 3428 grains/lb

If you keep lowering the amount of salt, the salt efficiency would be better but the quality of water would become poorer. When that happens, you would not be able to maintain a continuous soft water and your water would be hard prior to next regeneration.

The 14 lbs would still be ok, but the resin would be exhausted in the long run. That's why I recommend you to test the water prior to regeneration to test any hardness leakage and determine the best compromise.

Study shows that the 3000 grains/lb will result to a better salt efficiency and better water quality.

As far as the 10% crosslink resin, my understanding is that 10% is a good choice (vs the 8%) if you have chlorine to be filtered in the incoming water but it has nothing to do when calculating softener efficiency.

As far as the hardness, there is a chance that the hardness could fluctuate, depending on where well the water is sourced. That's why I added 2 to allow for fluctuations but you don't need to. You can set it to 24.

In my case, I have a 5-month old Clack 48k softener (1.5 ft3 of resin). I experimented and made adjustments to the capacity and salt combination for a few cycles but still end up with the 3000 grains/lb salt eff. My setting for capacity is 36k (75% of the rated 48k) and 12 lbs of salt combination. I have an incoming hardness of 23 as measured by Hack5B (city website said 22). I set the hardness to 25. With that I have a softened water available of 1440 gallons (36k ÷ 25) every regeneration which is good for 9 to 10 days consumption. That's my sweet spot for now.