Thanks for your audience. Photosynthetic rate varies from species to species and is limited by several biotic factors. Hence, it is not easy to attach a figure to it. Concerning the efficiency in relation to oxygen production, since plant themselves use oxygen during respiration, it is best calculated as net oxygen production which by all means is related to net productivity. Elevated carbon dioxide level has been found to increase photosynthesis in some species and also reduced respiration in some. It is still an active area of research.