Tokays come in different sizes: there are males that are giants and there are long but thin males; there are petite females and there are big, big females; juveniles are small and sometimes take up to two years to reach full growth.
10 gallons suits several of these: petites, juveniles, not yet full-grow tokays.
I have a rather large male who spends his days in a ten gallon with his female companion. Sounds cramped? About five nights per week he (and she) comes out and spends his time in a "for herps only" bathroom where he enjoys running about. He also spends time with us in the living room (he is tamed) enjoying TV. He travels with us several weekends in a month at reptile shows. Ten gallons is perfect for him in this situation.
I have a petite female in a ten gallon tall enclosure. This is her permanent home. She is not stark raving mad from her "small space", rather she is happy with multiple climbing areas, a strawberry pot and a sansaveria.
There is no one right answer in this situation. Experience tells you which works best. Larger is better but small quality can work.