I have to say this is a good idea, and i have thought of this myself. I thought of a ship larger than a GB, but less than a cruiser flying around with one large cannon, or 2-4 smaller but strong cannons with very limited hull, movement, etc.
Plus, for this to even be different, the guns range should be about 6K if not more. Also, maybe even a "Target" distance can be set, saying you might want the shots to explode at 3K, not the maximum distance.