Nice pictures - the pic on the right of the GSR head. On two-strokes, the area highlighted with the red arrows would be referred to as the "Squish Band" on a hemi head.More compression would make you more susceptible to detonation, but you can make more power (GSR head). The two heads flow well enough that the difference between the two is negligible.
Here you can see how the GSR (Right) combustion chamber differs giving you a higher compression ratio with a smaller chamber.
I've read Honda considers their head design to be "Pent Dome" and not true "Hemispherical". So, would the GSR just be further down the road of the "Pent Dome" design?