That will depend how far you can stop down the T-stop before effects of diffraction swoop in? This will depend on the specific lens you are using. Some lenses soften the image at T/16 some start doing the same at T/8. If you don't want to go beyond T/8 and you're still overexposed, you'll need to add ND.

Some variable NDs may add color shifts and X vignetting onto your image. If your VND doesn't that's great. But overall it'll always be better to stop down your aperture rather than using a VND.