I am currently running 215/60R16 tires on my 85 Tintop with manual tranny.  My trusted mechanic is encouraging me to move up to 215/65 or even 215/70; he says the Subie motor has plenty of power to handle the bigger rubber OD.  But I am not so obliged, here is my reasoning:  Number 1, I drive a LOT of twisty mountain roads and sometimes that include a long grade prior; I totally love the response and performance when in these situations, one of the main reasons I did the conversion.  Number 2:  Being a little OCD, having the speedometer and odometer even further off than currently (example, 62 Speedometer vs. 65 GPS) would just bug me.  Number 3:  Braking....yep, the larger rubber OD means reduced braking ability, simple mechanical advantage situation.  Number 4:  Rotational Inertia of more heavy rubber further away from rotational axis means harder to get going and harder to stop, so a little harder on motor and a little harder on brakes...I know, I'm getting a little picky on this one.

Sure, there might be some MPG gain (not that important to me, as it is I get a reliable 22 MPG on roadtrips).  Sure, when freeway cruising on long flats, could probably maintain higher speed, but that might be offset by frontal wind resistance which goes up by the square of speed, non-linear.  There might be some engine or tranny wear issues due to some lugging in some circumstances, and I know that is a no-no; Subie motors from what I have heard due to their fine balance and strong metallurgy are fine with running 4000 RPM for hours and hours at a time.

These are my current thoughts.  Any input?  Something I'm missing?  Whatever the cost difference between the tire sizes is pretty negligible I'm thinking.  The driving experience is primary, followed by the longevity of motor and brakes and tranny is my main concern.