Because perspective issues come into play with wider lenses, the normal practice for full body portraits is to use a lens with a normal field of view (FoV). This will require greater camera to subject distance but will result in a portrait that does not distort the features of the subject. Both of your lenses are in the beginning of the telephoto range, so a lens in the 40-70mm range, while considered a normal lens, is wider than either of your two lenses. The classic focal length for full body portraits is at around 50mm for a camera using 35mm film or a sensor that is the same size such as your D800.

Remember, perspective is determined by one thing only: shooting distance. Focal length is only secondary in that it determines the shooting distance for a particular framing. If you are using a 50mm lens on a full frame camera, to get the same subject framing from the same distance you would need to use a 33mm or so lens on an APS-C body. Both lenses will demonstrate the same perspective when used at the same shooting distance. If you used the 50mm lens on the APS-C camera you would need to back up 50% further to obtain the same framing. At that distance, the perspective obtained would be the same as a 75-80mm lens on the full frame camera.