It's your money. Get what you like. I think it is pretty arrogant to tell someone whom they do not know, that their camera(s) are "overkill" for what they do (clearly "trivial" work in their eyes). It's like telling someone who can afford it, that a Mercedes or Lexus is overkill for driving around town and short vacation trips. I'm mostly jealous of someone who can afford both. To me the D800E, and I'm fortunate to have one, is an instrument that is probably best for high resolution, detailed, "deliberate" work. That does not mean you cannot or should not use it for sporting events. The D4, and I really do not want one at this time, is an perfect instrument for fast, high quality work, eg sports. I am a former 4x5 and medium format film person who finally has a camera that can easily do most anything I want from macro, to landscape, to portraits and everything in between. If I needed to photograph a sporting event, I'd prefer a D4, if I had one, but could probably make do with the D800E or my old D700, which, though obsolete, still seems to work and to make pretty nice images, many of which are on people's walls.
Comparisons are great, clearly different tools excel in different areas, but unless someone's paying for it, no one has the right to tell you which camera to use for which purpose. I never did use the 4x5 for action work, by the way
Two quotes, one from Al Webber "Buying a Nikon and a roll of Kodachrome does not make you a photographer ..Just like buying groceries does not make you a chef," another from August Renoir, "Be a good craftsman, it won't stop you from being a genius."
Have fun, make images, do not worry about others' opinions.
Eric