You're right, I was thinking about momentum transfer when I started the question.
Thinking about the duration of the impact...I don't know if it's different or the same for the 2 spheres. Assuming the wall is not rigid and it can move, I can envision a scenario where impact duration is the same...
I assume KE is conserved therefore, the KE transferred will be the same. But intuitively, this doesn't seem correct. Seems like the object that breaks apart would transfer less energy than the object that doesn't. Any thoughts?