On the inside of your fuel cap it should tell you what the car needs to be filled with.

My car is an 08 WRX and it states that it needs to be filled with 98. Whether or not there is wiggle room there I don't know, but that is what I have always filled the car with. I've also had a tune on 98 premium now so wouldn't change.

EDIT: Cap only actually states premium so you should be fine with 95 if you choose. As mentioned though I am stuck on 98 as that is what I'm tuned for.