Native USB port speed not as expected?

[Icebuster]

dependence of DUE Native USB port transfer speed on data length

I'm working on writing a reusable Arduino <-> Python communications library for scientific instruments, and as part of that I would like to transfer data at high speed to Python running on a host PC. I tested the transfer rate from both the programming and native USB ports and don't fully understand the results. I tried transferring strings with 1 to 10000 characters (call the number of characters N). Each string was written with one call to Serial.print() or SerialUSB.print(), and read by a Pyt…