Ki Strike (magic) and Ki Strike (lawful) are for the purposes of bypassing damage reduction. Ki Strike (adamantine) also bypasses damage reduction, but it also treats the fist (or foot, or head, or elbow...) as being made of adamantine for the purposes of bypassing hardness - in other words, you ignore a hardness of 20 or less.
But, yeah. Sundering is almost always a suboptimal strategy for PCs. You're usually sundering your treasure. It can be useful if, say, the DM will let you replace the haft of a magical greataxe without any big, epic quest to get it re-enhanced, but, generally, not worth it. Disarm and Trip, or just plain hitting things, tends to be better.
