It is also easier to get a higher CR with a 2 valve head as the chamber can be smaller too.
To the contrary, it was harder to achieve very high compression ratios on the 2-valve Kawasaki Pro Stock engines at the time. This was due to the valve angle in the head and a large, almost hemi like combustion chamber. It was much easier to achieve desired compression ratios with Suzuki’s shallow “pentroof “ combustion chamber. That was one of the reason most of the field at the time used Suzuki 4-valve engine. The late Dave Schultz was the only one that was (somewhat) competitive with his Byron built 2-valve Kawasaki. NHRA changed the rules a few years after I left the sport and it became advantageous to use 2-valve heads. However neither the GS 1000 or Kawasaki’s heads supported the airflow needed for a 1500 cc engine. Hence the Vortex large port, large valve heads. I do not know how the valve angle and combustion size on those heads compared to the stock 2-valve heads. They might be shallower and lend themselves better to high compression
As far as 20k rpm, we will see that in Formula 1 next year since they are changing the engine rules from 3.0 liter V-10s to 2.4 liter V-8s. They are already exceeding that rpm on test engines… Currently, the V-10 revs to just over 19k and lasts (mostly) two complete race weekends.
Wolf