I bought two black Copic markers to test out the difference between the 100 Black vs the 110 Special Black.
On the left is 100 Black, probably the more common markers people would buy for black. On the right is the 110 Special Black. I drew the strokes on ruled paper.
Here's a closer look at the 100 Black.
And a close up of the 110 Special Black.
The strokes here are drawn on 135gsm cartridge paper.
Differences? From what I observed, the 100 Black is slightly darker. And the 110 Special Black seems to have a slight warm undertone from the close up picture.
The differences are minimal at best. Having said that, it might be worth a consideration which marker to get to pair with your warm and cool gray Copic markers.