More results...
Some observations...
• The processor-to-PC speed is significantly better with the m16u2 than the FTDI. That was my observation the last time I ran tests like these. The best serial speed I observed previously was with the Pololu Programmer (it includes a USB-to-serial converter). I did not test with the Pololu this time.
• At 1 M there is no measurable difference between "fast" and "slow". That was also true for the m1284 processor.
• At 115 k there is a significant different between "fast" and "slow".
• There is a very significant difference between 1 M and 115 k.
A 1 M slow no-LED bootloader would be a good path forward. The upload times are significantly reduced, there is no performance benefit from the fast bootloader, the slow bootloader frees a bit of space, and the no-LED frees a bit of space.
If there is anything else you would like tested or you want any details about the test just let me know.