I ran some tests Friday and finally got some partial stack kills. I did ten battles for each test. I attacked with three longboats (a 2* and two 1*’s) versus a 3* barque, a 1* barque and a 1* Dromon. First was a stack of three attackers vs. a stack of three defenders. I lost a total of 21 ships and sank a total of 21 ships. 40% of the time I won control of the sea zone. Then I did three singles vs. a stack of three ships. I lost 19 ships and sank 18, but I gained control of the sea zone half the time. Finally, I attacked with only one ship against the stack of three. I lost 8 ships and sank 11, but only won control of the sea twice. The defenders never tried to flea. This is hardly conclusive, but seems to indicate that neither large stacks nor singles have a clear advantage.
Still, IMHO.