"The Mobile Intel® GL40 Express Chipset features channel DDR3-667, DDR2-667, DDR2-800 and DDR3-800 memory support, 800 MHz system bus, and PCI Express* x1 I/O ports, Serial ATA, and Hi-Speed USB 2.0 connectivity."
Ok, I was confused by this document. So 800MHz are supported, but you'll only profit from it in a few situations. CPU intensive tasks can't use it because of the 667MHz FSB. The only component that will be fed with 800MHz is the GPU.