Debating between two smaller systems (2 and 2.5 tonnes) vs. one larger system (4 tones) for a 2,600 sq. ft. 2-story home. Was leaning towards the 2-system route so that would preserve closets on 2nd floor and also so that would have 2 zones (only heating upstairs at night, only cooling downstairs during day, etc.) however would this 2nd reason also be possible with the larger, single unit system route? In other words could the supplies that extend down to the 1st floor be controlled separately from the supplies to the upstairs?