6GB vs 4GB - why 6GB slower bandwidth ?

[eva2000]

Just installed Win 2008 Enterprise 64bit for a run

Strange that 2x2GB (4GB) is slightly faster than 2x2GB + 2x1GB (6GB) even at same timings ??? And since these results also appear in memtest it ain't just a Win2008 issue. Maybe Asus Blitz Formula related ?

Using 2x2GB Gskill PC2-8000CL5D-4GBPQ + 2x1GB Gskill PC2-8500CL5D-2GBPK so both kits are non-Micron D9 based

• 9x333FSB 1:1 333Mhz 2x2GB 5-5-5-15 3-42-6-3-3 memtest bandwidth = 3500+ MB/s and Super Pi 8M = 3m 24s
• 9x333FSB 1:1 333Mhz 2x2GB + 2x1GB 5-5-5-15 3-42-6-3-3 memtest bandwidth = 2025 MB/s and Super Pi 8M = 3min 32s
• 7.5x400FSB 4:5 500Mhz 2x2GB + 2x1GB 5-5-5-15 3-52-6-3-3 memtest bandwidth = 2994MB/s ???
• 7.0x429FSB 4:5 536Mhz 2x2GB + 2x1GB 5-5-5-15 3-52-6-3-3 memtest bandwidth = 3212MB/s ???
• 6.5x462FSB 5:6 554Mhz 2x2GB + 2x1GB 5-5-5-15 5-52-7-5-5 memtest bandwidth = 3186MB/s ???
• 6.5x462FSB 5:6 554Mhz 2x2GB + 2x1GB 5-5-5-15 4-52-7-4-4 memtest bandwidth = 3249MB/s ???
• 6.5x462FSB 5:6 554Mhz 2x2GB + 2x1GB 5-5-5-15 3-52-6-3-3 memtest bandwidth = 3315MB/s ???
• 9.0x445FSB 4:5 556Mhz 2x2GB + 2x1GB 5-5-5-15 3-52-6-3-3 memtest bandwidth = 3329MB/s ???
• 7.5x534FSB 1:1 534Mhz 2x2GB 5-5-3-15 3-52-6-3-3 memtest bandwidth = 5872 MB/s

Any ideas why it 6GB config is clock for clock slower ???