Do you want to know rate of moisture loss, Boofer, or just some anecdotal guidance?
Rate of loss depends on form factor, room RH and how heavy a coat you put on. Generally, if you're not able to go 90-92% RH and are stuck in the 80s RH, a moderate paracoat applied with a brush will slow down moisture loss by 40-50%. It is still rather permeable. A thicker coat will help more.