CPU test performance drops when RAM increased from 4G to 8G

[petercdickinson]

I'm getting a puzzling result with PerformanceTest 8.0 running on 64-bit Windows 7 Embedded Standard. This is running on an ASUS motherboard fitted with an Intel Xeon E3-1230L v3 quad core CPU clocked at 1.8GHz. I'm getting an unexpected performance drop in the CPU tests of between 8% and 13% when I fit a pair of 4Gb UDIMM modules, compared with the same system using a pair of 2Gb UDIMMs. According to the specs, the UDIMM modules are supposed to be the same speed. Also, in some of the CPU tests I see a similar performance drop when comparing against the same system with a single 4Gb UDIMM installed.

Why would installing more memory cause a CPU performance drop? I'm not seeing this drop in the memory tests.

[David (PassMark)]

Maybe the system drops out of dual channel memory mode? This would definitely be the case when going to 1 RAM stick.