I have a P5Q Deluxe and a Gigabyte GA-EP45-UD3P (and others) derived from the similar chipset. The Asus is a bit more particular, but don't anticipate the Gigabyte (you didn't say which one and not all are created identical) to run them perfectly. The modules are designed to sprint at 4-4-4-12 2T, 2.1V when 2 modules are installed. When mounting 4 modules, you need to run them with more voltage (I wouldn't because they require too much voltage) or, as I suggested, untie the timings. You could also run them at 667 MHz and you perhaps won't notice the presentation dissimilarity. You're not the only one having matters with 8 GB of CM2X2048-6400C4DHX.