I did test. This is my results:
buffer 48: 121kByte/s=0,95Mbit/s
buffer 256: 129kByte/s=1Mbit/s
So, reading speed of SerialUSB is not very good.
You can look at comparing test results from the Internet:
It's very terrible that Arduino Due has so powerful hardware and so not optimal libraries.
Guys, let's fix it pls.
I found one solution here Faster SerialUSB read - Arduino Due - Arduino Forum
But I haven't so deeply knowledge to change libraries and provide it for all.
Can anybody from Arduino's experts optimize SerialUSB for fast reading?
Thanks in advance!