I'm pretty sure the default damage is 20 not 10.
Aside: Part of the reason even a 5% bonus to strength, in an otherwise even battle, is because you not only have a slightly higher chance to win each round, but also have to win less total rounds. Y'see, you will be doing 20 or 21 damage (5 round victories needed to win) while the opponent will be doing 19 or 18 (6 victories needed to win).
So, here's a question I've always wondered... when you have a 'chance' to do a first strike, what is the % of the time you actually get to do it? Is it static?