Even though they look similar in the bottle, it turns out that they're pretty far apart on the grey spectrum. S&G is clearly a khaki-tinged grey, whereas Dove is very much towards blue. The bottles look so similar, but that just goes to show - you can't judge a polish by its bottle. S&G is on middle and pinkie, Dove is on ring and index.
As you can see above, it's hard to tell them apart in direct sunlight, but it's obvious once you see it in the shade. Dove is definitely blue-tinged, and since I love grey-blue polishes, this is sure to be a favorite of mine. S&G is more nude/tan-toned, which will make it great as a neutral when you're not sure what to wear. It's great as a basic grey, but I don't think it has the extra stop-and-take-a-second-glance color interest that Dove has.
Application-wise, Skull and Glossbones was simpler. It took 2 coats, but I put 3 on for comparison purposes. Dove took a good 3 coats, and I had to do a fourth on my index because i smudged it before it was dry.