I assume your G74 is not running those 4 sticks at their rated 1600MHz speeds? You can double check this with memtest86+ : download this(http://www.memtest.org/download/4.20/memtest86+-4.20.iso.gz) and burn to disc; boot disc and look at the detailed info and specs displayed on the screen while the test runs. Let run thru three full passes of the whole testing suite: if error free your sticks are good. If even just one error is found you have to narrow which stick it is in: reboot with only a pair in there and test: repeat and narrow it to the one stick. Then RMA the whole set with Corsair.

You will probably find that all 4 sticks do not run at 1600MHz, but at 1333MHz; however,two sticks installed are detected at the faster speed correctly as the core i7 sandy bridge is supposed to do. This is a commonly discussed problem with all G74s here, and the only viable solution is a new BIOS from ASUS. If ASUS will ever release a BIOS fix for this problem (which would be incredibly simple to solve) then we all win; otherwise, you can try BIOS editing yourself (you risk bricking the machine and RMAing it to ASUS for restoration, but I believe some people on these forums have solved the problem with home BIOS mods).

My advice: leave it alone and enjoy the 16GB at 1333MHz until a fixed BIOS comes from ASUS. YOu will not notice **any** difference in real world performance between 1333 and 1600 MHZ: the difference only shows up in benchmarks, which are synthetic and unrealistic. And we didn't all buy G74s to run benches on them, did we?