When checking my digital speedometer reading against the analog speedometer, I notice that 70 on the digital one looks like 72 on the analog one.

If I go into the diagnostic menu in the BRZ's headunit, it'll also show my vehicle speed probably based on GPS. That's always reading -1 or -2 mph from what the digital speedo shows (so anywhere from 68 to 69 mph when digital speedo says 70 and analog speedo looks like 72). All on stock tires.

I can't help you.