I dont think ive ever really paid too much attention to it greg, its an interesting question though, and i certainly cant give any technical advice on why it would be different for the different beans, i would imagine the CO2 output levels would be influenced by a lot of things including all the processes from the origin of the tree right through to the level of roast, and even the climate in which they are degassing, the moisture level in the original raw product, etc etc.
Just a quick one on a side note(i dont want to hijack the thread) do the valved bags seep(for lack of a better word)CO2 without pressure? as in will they bleed off CO2 before the bag is inflated, i would have thought so, are you seeing a visual inflation Greg or is it your sense of smell gauging the degas amounts?
I know i havent helped........sorry :-[
interesting topic though :)