Well Stated!... Nikon (and personal experience from working at Nikon) places the uses of the D4/D5 (and follow alongs) differently from the D800/D810 group. The D4/D5 are for sports, professional field work that requires a rugged camera body and the photographer doesn't care about the weight. The D4/D5 have high speed shooting, extremely good low light capabilities etc. The D800/D810 is designed for high end photography and video. It is a good choice for landscape, real estate, portraits, tripod shots of offices and annual report photos. While the D4/D5 series is heavy, it is designed to allow a photojournalist to travel into the boonies without giving a lot of worry to protecting the camera. This goes to the adage of having the correct tool for the job. While the D800/D810 does well with video, the D5 has it beat in low light video. In addition, the D5 is the first Nikon camera to incorporate radio frequency control of the new top of the line Nikon SB-5000 radio frequency flash. Note: the other Nikon Speed lights (SB-500, SB800, SB-900, SB 910) all use a built-in light receiver on the side of the strobe that receives a signal in the initial flash of the controlling strobe (either another SB flash unit or the built-in flash on the camera in control mode) to activate, control and shape the light from the other strobes. Typically, the other strobes can be in 4 groups with each group being able to have individual control of +or - EV. Each grouping can have almost any number of strobes in it to control and shape the light in the photo. I use the system often with as many a 10 strobes. (Note: the photographer shooting with a group of other photographers can choose a "channel" for his/her camera and strobes to be on so that they don't interfere with or setoff another photographer's remote strobes in an event. (I use the ability to have multiple strobes on a shoot as a method of getting (extending) the range of illumination beyond the reach of one strobe (like placing strobes down both sides of a cathedral in order to get balanced light from back to front, beyond the normal reach of one strobe. While both the D8xx and D5 will do this, the D5 currently takes advantage of the newer technology on the radio speedlight verses the light actuated speedlights. My suggestion is to evaluate the pluses and minuses of each of the cameras and make the decision based on your needs and wants. Personally, I would have a D5 and a D8xxx in order to cover both needs. (but this is a large expense). If you already own a D8xx and are looking to add, I would look at the shutter count on the camera I already owned and if it was reasonably low, spring for the D5. If the D8xx shutter count was near the maximum expected, then I would think about replacing it (keeping in mind that if you purchase the D5 then your new camera would take a part of the shooting load from the current D8xx). Again, only you know how you currently shoot and what you are wanting to shoot. SO, only you can make an educated choice on which way to go (understanding the limitations and advantages of each camera). Personally, I have a D70s (keeps my wife off of my better/newer cameras), a D7100, and a D610. The D7100 is a DX which easily uses the same FX lenses of my D610 which allows me to keep a long lens on the D7100 and a wide lens on the D610. Both have comparable resolution (D7100 is 24.1 and D610 is 24.3 although the D610's pixels are larger by about 30% than the DX camera's). I staggered the purchase of the D7100 and the D610 so that the D7100 has about 1/3 more shots. While the D610 is newer and the number of shots per job have been reduced by sharing the workload between the 2 cameras, I will replace the DX camera in another year or 2 and give it to my wife (retiring the D70s). Then in a few more years, I will do the same on the D610, getting what ever the follow along is at that time, and donate that camera to the wife. Note: We shot a wedding last weekend and she ended up using the D610 while I was using the D7100. Everyone has to make some concessions in order to maintain peace in the household.