Are BIOS settings already optimised when the PC arrives?

Yes. If a selected configuration requires specific BIOS or UEFI settings, these are set and tested before dispatch. This includes, for example, memory profiles such as XMP or EXPO, or options from a booked overclocking package. For motherboards whose BIOS setup offers a corresponding import/export function (this applies to almost all motherboards; the only exceptions at present are AMD Threadripper models), the settings are also saved as a BIOS profile file on a USB stick provided with the motherboard.