Given the combination of scion to rootstock, they may top out within a few feet of each other in terms of height and breadth. You will still need to open up some space for light and air most summers - that is the case with my English Morello sour cherry on Gisela 5, which might get to be 9 feet tall. Quite small as cherries go.
I'd expect your trees to top out 12-14,' but that depends on several factors.
> I have a sweet cherry cv. 'Lapins' on Gisella-6 dwarfing rootstock and a sweet cherry cv. 'Rainer' on Zaiger. Northeast; New Jersey.
> If left unpruned, what is the potential size (height/width) of these trees. Unfortunately, they are two differing cultivars of two different characteristics of vigor themselves, so that adds to the uncertainty additionally.
> I feel that, despite what is frequently advertised by some nurseries, they will not just stop at 12' if unpruned; and that they will yet never get to 70' like a P. avium seedling on its own P. avium roots.