Well I always wondered what that "Fastest System Performance" thing actually meant. I mean, we all want fastest performance, don't we? But that could be an explanation:
- "Normal" system performance means the BIOS times the memory as you tell it to
- "Fastest" system performance assumes you are a fool to select such an option, and the memory makers know better, so it ignores your BIOS memory settings and always uses the SPD information
I know this sounds cynical, but it seems in accordance with the symptoms.