The Nikon D810 is now one of a number of full frame options in the Nikon line, thanks to the revival of the D750 line. So where does the D810 fall? The D810 offers a high resolution 36 megapixel full frame sensor wrapped in a weather-sealed magnesium alloy body. The autofocus system boasts 51 points and an upgraded processor gives it a 30 percent boost in speed over the older D800. Video quality should be solid as well, though without 4K capability, at 1080p and 60fps.
It's a bit easier to talk about what the D810 doesn't have. With just a 5 fps burst speed, it doesn't offer the high speed performance of the D5. Wireless and GPS are available, but as add-ons that you have to purchase separately. There's no big extras like a tilting LCD screen. And while the D810 offers a more compact body than the D5, it's still a bit on the heavy side at 2.8 pounds.
The mid-range full frame DSLR arena is becoming increasingly competitive. The Nikon D750 bests the more expensive D810 in a few ways with a tilting LCD and wi-fi, though that means sacrificing a bit of resolution, a slower maximum shutter speed and a lower flash sync speed. Canon's EOS 5DR offers a much bigger resolution with a 50 megapixel sensor, though has nearly half the battery life and no tilting screen or wi-fi.