1.7 or 2x teleconverter on 70-200 f 2.8

I have a D800 and 70-200 2.8 lens. Need a teleconverter for wildlife shots while traveling (Yellowstone in winter, Alaska next summer). I know in most cases I can crop with the d800 to get a "little more reach." But will the 1.7 cropped be any sharper than the 2x? I'm not taking bird shots much. More static subjects that will let me stop down form better IQ. Anyone compare these?

Thanks for the help.

Greg