Forgot to add in: They just encountered each other in a grassy field and Kabuto doesn't have Edo Tensei.

Kabuto, high diff.

If it's eWA Gaara then SM Kabuto low diff

If it's late WA Gaara then WA Gaara low diff

Gaara does not have that big of a difference in strength between then. This is WA Gaara (vs. Madara).

Yes there is a difference.

Kabuto wins using sonic genjutsu.