I've had my P5B-Deluxe for over a year now and I'm pretty happy with it. Over the last couple of weeks I've upgraded my system to 8GB of RAM for use with Vista x64. Previously I was running with 4GB.

Memory is Corsair XMS2 CM2x2048-6400 C5. I also have an E6400 OC'd to 408FSB and 1:1 memory ratio. Last year I remember running Everest memory benchmarks and got ~12,000 MB/s read, which was pretty close to the max given my FSB.

Since then I've changed BIOS versions and other settings, and for I while I noticed my boot screen says PC2-4300 when it's OC'd. If I revert to defaults it says PC2-6400.

Now running Everest today I get about 7,638MB/s memory read, which is inline with a standard FSB, but not my 408MHz FSB. Everest and CPU-Z both show 1:1 memory ratio.

Any ideas on why BIOS says PC2-4300 upon boot and my memory read benchmarks don't reflect the higher FSB bandwidth? This is with the 1226 BIOS, and also happened with previous versions as well.