http://www.bjcp.org/2008styles/style13.php#1b
Ask your friends to taste it with these guidelines in hand. This is how the comp judges will evaluate it. The coffee in a SS is usually a favorable note, and not the dominant theme, so it depends on how your coffee comes across. It should not be "all coffee" so that roasted barley and chocolate notes are lost. Or so coffee that the "sweet" is outweighed.
Specialty is more of a "called shot" category. What the brewer puts in the "entry info" needs to be detectable to the judges or it's dinged. And the base category is considered too, so a "Coffee Stout" would be judged a little looser than a "Sweet Stout with coffee." In the latter, the sweet/lactose would need to be noticeable since it's part of the base style.