I'll tell you what. I tried 20/50 in Vixen's slant 6 about a year or so ago, because I had some. It made the engine very difficult to idle when it was cold and you could FEEL it. I could feel less power going down the road. I was blown away, but that's the truth. I ran it for about a month when our next payday came around and changed it back to the Motorcraft semi synthetic 5/20 with Rislone ZDDP additive and it made a world of difference. Had anyone told me that story before it happened to me, I wouldn't have believed it.
