A lethal first strike? Surely you jest. This is Bleach we're talking about.
Curiously enough, Shunsui is exactly the guy who goes against that. Look at his fight against Starrk and you'll see that every time he actually takes the offensive he tries to kill his enemy. He even betrayed the most sacred rule of shonen fights and attacked Starrk while he was talking to Lillynette.
Despite the way he acts, Shunsui is pretty much the only character who takes his enemies seriously and tries to kill them all the time instead of wasting time showing off. Even in this fight you can see the times he attacked Lille were all attacks that would be lethal if they connected.
That's why I don't bother if this is a long 1x1, he is a fresh air in Bleach just like Mayuri (although for completely different reasons).