The intake valve close event has a HUGE bearing on ability to run pump gas. Sport bike engines can run their sky high compression numbers because they have 300+ degree cams that make power into 5 digit revs. This puts the intake valve close event long after BDC and keeps the DYNAMIC compression low, even though the static compression is extremely high.

I've heard that 9.0 dynamic compression is an approximate limit for aluminum head engines on pump gas. You can go higher, but you really need to know what you're doing.