I shoot Canon and have a decent choice of L glass. It's great stuff, but like all things unless you are in the very top percentile of professionals (which I am NOT) the difference between Nikkor and Canon L is going to be insignificant for the same class of lens (prime, zoom, aperture etc.). My favourites, for sheer image quality out of camera are the 200mm f/1.8 L (old, wonderful sports lens) and the 100mm f/2.8 L Macro IS. Friends with Nikon get some great shots too in similar conditions.
When it comes to my P4 I am still getting to grips with the settings and have not spent enough time with the DNG files, but I am really impressed with its still and video quality considering the physical challenges of keeping the camera stable and the size of the optics.