Stomatal density determines the potential surface area for movement of CO2 into the leaf, thus driving photosynthesis.  However, it is the degree of openning of the stomata which determines the actual flow of CO2 into the leaf.  A plant with high stomatal density will have a higher potential rate of photosynthesis, but the plant will then control the rate of photosynthesis by managing stomatal aperture, as a balancing act between inflow of CO2 and outflow of water (transpiration).

I think stomatal apperture is more important in determining the rate of photosynthesis as it has a control depending on the environment.  Whereas the stomatal density is a genetically inherent character.

Ok do you think that reduction in stomatal density as EPF2 lines which has been generated( less number o stomata) would affect photosynthesis negatively or no differences since stomatal aperture is more important?

Though in principle I agree with the answer of Mark Andrew Skewes, however, gaseous exchange also occur through cuticle. In short there is no simple answer for your question.

Ok but is their any evidence which prove that gas exchange through cuticle significantly influence photosynthetic rate?

It would have been easier to answer this question if discrete analysis can be conducted in order to determine the % contribution of each parameter to photosynthetic rate, A higher stomatal density as previously stated should potentially increase photosynthesis theoretically  but the plant's response to gaseous flow is via the regulation of the stomatal aperture. It therefore means that irrespective of the stomatal density, gaseous flow is still crucial and can largely be controlled by the regulation of stomatal aperture. However, it is also important to consider cuticular diffusion which is largely influenced by cuticular resistance and can be beyond physiological regulation by the plant

Both are important. I want to drow your attention to the experiment that we did before. We used chlorophyll fluorescence under non pbotorespiratory conditions. In this technique the PSII efficiency correlate with stomatal opening and density. We used low VPD to ensure higher stomatal aperture and high VPD to ensure lower stomatal apperture. In general there were no difference between two treatment since lower stomatal apperture compensated by higher stomatal density in high VPD plants. Our experiment showed that higher apperture in low VPD plants resulted in huge water loss without subbstantial change in photosynthesis parameters. On the other hand high VPD had lower aperture without difference in pbotosynthesis with low VPD plants while they keep internal water means saving more water. In general for best photosynthesis plants do not need to fully open their stomata. As a rule higher stomatal density correlate with lower size of stomata and these characteristics means faster response to environmental factors which is a very important factor for water use efficiency in plants. Therefore I am more fan of stomatal density.

Consider the cuticular exchange of CO2 across the mesophyll and atmosphere is constant  factor for any given leaf lamina. The major component which restricts photosynthesis is stomatal aperture size than stomatal density. However, water use efficiency (WUE) of any plants  related to lower aperture size or better control by guard cells. Stomata frequency or density  is also important for overall photosynthetic rate  but comes as a second major factor only. For instance  though your experimental plant has higher density of stomata due to adverse climatic conditions all the stomata may close simultaneously results in low  or nil photosynthesis. 

Annamalainathan

But we did not see low Pn due to higher stomatal density. I just mentioned that they response faster to environmental cues.