Your calc came up with sensible and latent btus,you need equipment that is rated to cover each of those numbers
ARI and manufacturers ratings are for what the equipment will produce at specific indoor and outdoor temp.
Charts usually show various OD temps and the capacity for each.
Indoor is at 80° F,footnotes on the chart may tell you this.
For every degree indoors below 80 the sensible capacity is to be derated ,835 sensible btus for each degree below 80 ,per 1000 cfms of air flow.
So, 835 btus X 12 degrees X 1.2(for 1200cfms)= 12,024 deuct in sensible ,and 12,024 increase in latent.
With the new latent number,half the excess latent capacity(over the latent load calc) can be added back to the reduced sensible.
Seems you calc is off since you have a 3 ton(I think) or you weren't running it at 68° F,in the past.