You mentioned storage and speed and these are two different things.
Storage wise, for general user, compressed lossless at 45MB would be good enough. Visually, hard to see difference in quality between 75MB file and 45MB file.
For speed, if you do not need to shoot a large number of frames per second, get at least a 4X reputable SD card so that you can still shoot decent video with the D800, as you will not use the higher speed SD card to its full potential anyway. Point to note, get a REPUTABLE SD card as 4X speed is the minimum for HD video recording, at least according to my experience.