Have 250,000 miles on my 2001 V70 non turbo, using semi synthetic and 87 Octane, I am retired and don't need to get anywhere in a hurry. If you're driving a non turbo, you're wasting your money on 89, or 91 Octane, change the spark plugs to OEM plugs and use 87 Octane. Of course, if you need to drive fast to the next stop sign or red light, then use 89 or 91 Octane. On the Highway there is no difference, unless you need to drive excessively fast.