It is going to interesting to compare these two new lens offerings. Identical focal lengths and apertures, very close in price ($150 USD more for the Nikon). If a larger mount diameter is going to make a difference in image quality, it should be apparent at these short focal lengths. We will see if the touted advantages actually make a difference in the real world. The Nikon is bigger, heavier and costs more... does it deliver more? BTW, I don't have a horse in this race yet... but I am horse shopping.
Glenn