If either is traveling at 10K mph it probably doesn't make much difference in space. You're either instant Swiss cheese or instant soup. If there's a nice blanket of atmosphere to burn through before it hits you, then definitely the gravel is the better option.
“If there’s a nice blanket of atmosphere to burn through before it hits you, then definitely the gravel is the better option. “
Good point. Your first point is also good.
Your first point suggests the boulder is the better choice because it, as compared with a spray of gravel, has less chance of hitting you.