rafscipio:
As you can see from the waveform related to the usb-dongle, actually IS possible to send many repeated trasmission separated by only 200us (not 1ms) over usb, and i saw the same with other device (similar to Arduino, with serial over usb) doing the same, which i used in my project before trying Arduino.I think that running 20 times slower, is an issue for every kind of project
I have no idea what your nice graphs are displaying - you have not said how they were produced. The graphs seem to show single pulses at intervals. But a piece of data is not a single pulse - so I have no idea what the pulses are.
Saying something is 20 times slower is meangingless without a context. When I was experimenting I wrote some PC and Arduino code that sent data in both directions and I timed how long it took to do 1000 loops. As I said already, the throughput was consistent with the chosen baud rate.
If you have some code that demonstrates the problem you perceive I will be happy to try it.
...R