tito-t:
sorry, but IMO your answer is ambiguous and vague.
They don't seem that way to me. And the easiest way to resolve the issue is for you to do some tests.
moreover, about
" (BTW, my msg buffer size is 64 bytes) What does that matter? It does not prevent you from sending more or fewer bytes."
it was you yourself who stated
"But be aware that USB can have a surprisingly low throughput for small data packets - i.e. less than 64 bytes.", so now you even contradict to yourself.
If you read carefully you will see that both statements live happily side by side.
If you don't agree then please explain your thinking.
...R