When was the compression of the 65 and 80 lowered, and how can we tell the high compression from low? (Short of turning it over... I'm thinking more about how to spot the high comp engines in the used market.)

I've read that OS Suprass 4 strokes have a higher cmpression ratio that Saito's and hence run better on lower nitro. I don't have the personal experience to know one way or ther other, but's it is an interesting difference if valid, and might sway ones purchasing decisions.