I highly doubt that you will notice any difference in quality. The idea of a faster 2.8 lens is that at it's "sweet spot" is likely f5.6-8.0 where the f4.0 lens will likely be optimized at f8-11. So, in practice, it's easier to work with difficult negative negatives that are over developed. But if you have a perfect negative and print at their "sweet spot" (where you can literally watch the grain jump up and hit you in the face through the focuser from corner to corner on the paper), I would bet my next paycheque you will not notice a difference in quality.