depends on how much range you need
PHEV means you charge the car and use like a pure electric car.
so if the manufacturer claims a new PHEV will go 70km pure electric when new (100% SOH)
that means a real world pure electric range of about 50km upwards
so 60% SOH for that car would be 30 to 45km.
if you mean when will it get to 0% SOH ... who knows
it's up to you and what your needs are and how much you are paying for the car
if the car is $1 with 0% SOH I'd still buy it
degradation - well ... crystal ball ... you'd assume if same treatment same degradation but i don't know
what i know is if you have lower capacity you will be charging it more ...
PS - drives a nissan leaf w 50% SOH