I don't think the NEX-7 will be anywhere as good as the 5N in terms of noise performance. While I will miss the handling and built-in EVF of the 7, image quality matters more to me. When the external EVF goes down in price, I will pick one up for the 5N. One of the good things about external EVF is that it can be used on the next model (hopefully) and can be sold separately if I later upgrade to one with built-in EVF.
In conclusion, I have no complains about the image quality of the NEX-5N. I am VERY glad to have bought it. Now, why didn't Sony just use this wonderful sensor on the NEX-7, or, make a model with NEX-7 body with the NEX-5N sensor and priced between the two? It will be a perfectly balanced camera in terms of handling and image quality.
Cranes -- NEX-5N & Leica-R Elmarit 28mm f2.8, ISO 400.