Just finished installing the new 3900X in my sons rig, replacing his 2600. His board is the Gigabyte B450 Aorus Pro.
The instructions on the Gigabyte site were not clear in the process so I thought I'd write some pointers to help anyone else....
As stated on the BIOS page you need to flash to F32 before F40, and apply an EC firmware update....
(I've assumed you already have the F32, F40 and mb_utility_ecfwupdate_B19.0606.1.zip downloaded)
1. Flash to F32 using Q-Flash
2. When complete, enter windows and open a command prompt with admin rights.
3. Run the 'ECFwUpdate.exe' and after a few seconds a box will appear advising to start the FW update.
4. When the EC firmware completes the system will go blank and restart and will have regressed back to the F1 BIOS - (there is no progress bar to show any progress)
5. Enter the BIOS, open Q-Flash and re-flash F32 - you will not be able to flash direct to F40 as it will state invalid checksum/image.
6. When F32 has completed flash again to F40 (it will be ok this time) and install the new CPU.
7. When it comes on, set the BIOS up as per normal and install the latest Radeon chipset drivers.
My son is using the bundled cooler and its all running sweet, his ram is 32GB C14 tridentZ @3200MHz, no problems so far.