20k on a Euro oil? Or would you go boutique? That is wild to me. But you have ideal operating conditions.I drive mostly highway actually. My drive from home to work (Niagara Falls) is 80 miles, basically 95% highway. And the other main drive is 50 miles to my girlfriends place, also 95% highway.
If I was driving 40k a year I would do 20 k intervals. I do about 25k a year so I am comfortable with 10k intervals, at least in my Civic.