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A good variable ND would give you options. My preference though (partly because I'm cheap, partly because I like knowing exactly how much ND I'm using) is to have a 3 stop and a 6 stop.
Most my Nikons have a base ISO of 200 also, and the 3 stops allows me to balance bright daylight at about f5.6. The nice thing about this is that I can still see through the viewfinder reasonably well. Example (1/250, iso200, 3 stop ND, f5.6. There's a scrim covering them in shade, so they're lit predominantly by strobe. The left frame is literally straight out of camera, no luminosity or saturation adjustments on the sky):
Then, when I want to shoot at large apertures, or really subdue daylight, I pull out the 6 stop ND. With this I always use liveview to focus and compose, since it makes the viewfinder so dark. I don't have an example handy like the one above, but with the 6 stop you could get that same exposure at f2.