I had a friend ironically in Indiana tell me he runs 15K OCIs with usually Valvoline synthetic in all his vehicles. He has a Honda Element with 450K now.They both probably do a great job of making an engine last a long time and keeping it clean. But I doubt the Valvoline would stand up to 20k miles as well, given the likely lack or less amount of PAO. Even so, you'll never see me run M1 EP 20k or any other oil for that matter. Even M1 EP is too cheap for me to run it to an interval with which I am uncomfortable.
I'd enthusiastically run either of these oils to the 7500 or so OCI's I run with my Pentastar. I don't think that would put any significant stress on either of them.
I should bother him more about it or get him to post here. I don't think he's ever done oil analysis on his stuff, though.