I definitely would not want the piston ramming into the cylinder head!(The rod would not live very long).
I recently set up a friend's 011 Gas Gas 250 - slightly more then 1/2MM (.024) squish and 200PSI cranking pressure (his specs).I'm personally much more concerned with the compression ratio and the type of fuel required to feed that motor then,say, squish for example.
My friend is still not 100% happy with the Gasser's motor and he is presently experimenting with different carbs and intake tract lengths.My own personal observation is that the reed cage assy appears small though I would suspect the Gas Gas designers went that route for a reason.