User blog comment:Reikyu/Plot Armor Part 2/@comment-76.168.15.61-20150328025210

Most likely the damage formula for overkill hits is Math.floor(Math.random * (Ship_max_HP * .8 - Ship_max_HP * .5)) + Ship_max_HP *.5 Basically 50% up to but not including 80%

What this would mean is Yuudachi (31hp) is better than Shimakaze (36hp) :

Under this formula, Shimakaze has 0% chance of yellow, 83.3% of orange, and 16.7% of rekt.

Yuudachi has 5.4% chance yellow, 86% of orange, 8.6% rekt.

Since events are usually what people worry about and the biggest threat to thoses sorties in terms of destroyer hp is being one-shot not chip damage, it seems Yuudachi has the upper had buy quite a bit. Also, marrying Yuudachi would bring her hp to 36, and but this make her weaker.