Oh well, I already ordered some 2 oz plastic. I did call DuPont, however, and they gave me a number to Material Concepts, who recommended "Hard Structure" type for tent floors. I see this is just type 10:
http://www2.dupont.com/Tyvek/en_US/products/structure_types.html Old news, I guess. All Tyvek is gas permeable by its very nature.
I have read about others adding a coating, but that it peeled off after not too long. I have some "camp dry", that is 13% silicone, which I think would result in the same.
Yes, the ground cloth, itself, would dry quicker, if it is gas permeable.
If you have any ventilation at all you shouldn't have any condensation problems.
My tent has good ventilation. I will be trying Tyvek after my 2 mil plastic is worn out.
Sorry if I am boring anyone to tears.