A couple things wrong here:
1) Your memory is clocked correctly: 665MHz at Double Data Rate (DDR) =1333 MHz, which is what the G74's BIOS will clock the RAM down to if it detects 4 sticks installed, regardless of their rated clock speeds. ASUS has not released a BIOS update to deal woth this, and in fact has not explained why the G74 does this, but the problem has been extensively covered on this forum. I think its a safety thing: since 4 sticks will require more power from the IMC to address than 2 sticks, the IMC will get hotter. Higher frequencies only increase temps and hence the problem. Since the IMC is integrated on the CPU, the heatload from the CPU will increase and may overwhelm the notebook's cooling system, which is already finely balanced at stock specs.
2) You have an Extreme Edition CPU in your rig, which are 55 Watt beasts. You're already beyond the 45W limit that the G74 was balanced around, and you'r likely stressing the cooling capabilities of the G74, and maybe even your power brick. I am not surprised the thing is being flaky.
If you want 16GB at higher clock speeds, try 2x8GB sticks. My advice is to stick to 1333MHz sticks, and not be fooled by manufacturers touting the high-performance gains from higher clocked memory (i.e.1600 or 1866MHz): it simply does not amount to measureable performance gains over 1333MHz sticks in real world usage of your computer. Only if you are a competetive benchmarker would you want that stuff to give you a few % edge. And no one who owns a G74 as their primary computer is a competetive benchmarker.
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G74SX-CST1-CBIL, i7 2630QM 2GHz
32GB DDR3 RAM @1333MHz
GTX560M 3GB DDR5 (192 bit)
17.3" LED 1920x1080
Sentelic TP, BIOS 203
Debian Linux Wheezy (Testing) Kernel 3.2, NVIDIA 295.40