If the file is stored as immutable data, public or private is the same. The only difference is the datamap encrypted or not.
First upload test: 94.5KB/s. (70MB)
Second upload test; 112,4KB/s (91,6MB)
Both as public data (MP3 Albums)
Resend second test as private, so chunks stored: 138KB/s
I think that the relay node is the bottleneck in several cases.