So I will find that info in boards.txt.
OK ... here a section:
uno.name=Arduino Uno
uno.upload.protocol=stk500
uno.upload.maximum_size=32256
uno.upload.speed=115200
uno.bootloader.low_fuses=0xff
uno.bootloader.high_fuses=0xde
uno.bootloader.extended_fuses=0x05
uno.bootloader.path=optiboot
uno.bootloader.file=optiboot_atmega328.hex
uno.bootloader.unlock_bits=0x3F
uno.bootloader.lock_bits=0x0F
uno.build.mcu=atmega328p
uno.build.f_cpu=16000000L
uno.build.core=arduino
As I read, the fastest is 115200 baud. That is for the UNO. But what about the ATMEGA329P with bootloader chip sold online... What is the typical speed for those chip with the bootloader ? Maybe it depend what board I select at the IDE level.
Nice to know...Anyway, thank retrolefty.