D800 vs D3s
D3s for close-ups, fast moving objects and shooting in low light.
D7100 for landscape, long distance, good light. Resolution of D7100 is significanlty higher than D800.
And the good thing, you don't get unnecessary large files. D7100 with 24MPx2,25 equals FF of 54MP.
For wide landscapes I use Photomerge in Photoshop and usually merge 2 or 4 images.
Missing something? For studiowork/portraites I guess D800 would be the better camera.