At these velocities the projectile will very violently explode, I think that it will have a decent spread rate. It can also be handwaved as not only the area of the ship that is physically touched by the projectile, but also that is destroyed by the shockwave of the armor being pushed out away from the projectile to make room for it.
However, at this speed, say, an impact speed of "just" 1000 km/s, the projectile would also take just one tenth of a millisecond to pass the entire ship.
As far as i know, and I openly admit that I really don't, the detonation velocity of a strong nuke is at best half that.
So, if you hit the target with a metal ball large enough to penetrate both sides of armor if it would
not disintegrate, the lowest speed that still achieves that would have the most devastating effects, destroying the ship.
Go too fast, and the shell exits the other way before expanding enough.
For example, if we calculate shell expansion at 750 km/s in an airlike atmosphere, which I think is pretty generous, then if the impact speed is above 2000 km/s, the effect would diminish.
Interesting, more power might not always be better.
As for the G question, that would mainly mean that if a whale was to jump into space, it would require a heavier ship to contain water, and have a lower max acceleration?
Isn't that also a question of size, as with the mouse?
Currently Aurora only models beings of roughly humanoid shape....
Also, it should be mentioned that the ideal gravity for a being isn't necessarily the one you get on your homeplanet.
Humans would probably function better at 0.95 g.
The problem so many people get back problems while aging is that our spinal column, more precisely our intervertebral discs, aren't made for this kind of strain, especially not over the life span we experience.
However, one could use a very slow acceleration during cruise as means of artificial gravity.^^