Inspiron 530 BIOS 1.0.12 memory performance degradation

Prior to updating from the 1.0.10 BIOS the (Vista) Windows Experience rated the original equipment 3GB of CL5 667 RAM at 5.7.  In anticipation of installing 4GB of CL5 800 RAM I updated to the 1.0.12 BIOS because it doc's correcting memory mapping for equal to or greater than 4GB.  One would assume this applies to 32bit Vista because it is available under that qualification.  After updating from 1.0.10 to 1.0.12 I updated the Windows Experience ratings prior to swapping RAM.  The memory rating dropped from 5.7 to 5.4 on the original equipment RAM (3GB CL5 667, aka. PC2-5300).  I attempted to regress to 1.0.10 however Dell now prohibits BIOS regression and the flash terminated.  Being stuck with 1.0.12 I installed 4GB of CL5 800 and updated the Windows Experience.  The memory rating increased from 5.4 to 5.5.  This is as expected however the initial loss on the original RAM after the 1.0.12 update indicates the 1.0.12 BIOS might have defects of some sort which render a performance degradation.  Be interested if anyone else has made this observation.  Note that the 1.0.12 BIOS also doc's microcode updates but doesn't spec for which processors.  The subject 530 has a Q6600 and it's possible there was a microcode update where some Errata (bug) was resolved by incorporating a fix in the microcode.  Wouldn't be the first BIOS nested fix of a processor bug that rendered a performance hit.