I don't remember. 

 best bang for the buck. longer battery life then 6. pro has a better camera but you're on graphene so does it really matter? just my 2 sats 

 Is it durable even though it’s made of plastic? (6a) 

 i think so. throw a case on it, it gets slippery if you have wet or sweaty hands. 

 I have a 6pro, wife has 6. Both have held up under Graphene. Good phones.