Where could one find a feature list or change log for Phoenix Bios? How would one compare and contrast versions? My search of the company's site and web have turned up very little.
F.3D and F.39 if numbered hexadecimally are separated by four versions. The only know variation between mentioned versions is that the fan algorithm has been changed from previous versions.
I doubt you will be able to find this information.
Typically, motherboard manufactures sign a NDA with the BIOS companies and have access to source code and binaries of the latest versions. They are able to release updates at will, however the version numbers do not always add up and they are usually only released to fix problems as and when they are found.
You are unlikely to find a complete changelog for any BIOS but simply see what the new release directly fixes. For example from a random Asus motherboard:
However, remember, you are a customer and they want your business! You have nothing to lose by emailing and asking them.
the Phoenix BIOS version is irrelevant, it's only a platform. you will have to check with the motherboard manufacturer, most of them update a changelog for their BIOS upgrades with the motherboard specification sheet. it's up to the manufacturer which features they make accessible for a particular mainboard. so, even if 2 motherboards have the same Phoenix BIOS version, that doesn't necessarily mean they do have the same features.