The size of the pot depends upon how much there is in terms of live roots. They will be whitish gray to tan and firm. The hollow, mushy dark brown/black ones are dead.
You always pot according to the size of the root system, not according to how much vegetative growth there might be.
If you overpot expecting new roots to fill this big pot, it easily leads to watering issues. If I was going to buy new shoes and my feet require a size ten, I would not buy size 12 hoping my toes elongate!!
