Test firing from a ground bench. It's capable of striking targets on the Moon from the launchpad at just shy of 5200m/s. If you miss, it'll exit Earths SOI and will go quite close to the sun so you could theoretically nail Mercury and everything in between as well.
It's not the be and end all, as you say, kinetic energy doesn't matter in this game. One object tends to only break one object regardless of how fast its going. I fired it at my Komodo rocket and it cleared the side engines and a few tanks out but not what a projectile at that speed should be doing which is cutting things in half and going out the otherside.
Yeah, if the target is harder than the projectile then it should just shatter on impact. That's usually the best way of stopping bullets. And also correct, at that velocity it should be going right through its target like a PaK88 through a Sherman