The difference between 1333 and 1600 MHz is so small in real world applications that its impact will not be measurable in test to test (that is, the variance in test-to-test scores will be more than the gains made by going to 1600 over 1333). And if you stuff your G74 with 4 sticks of 1600, it will downclock to 1333 anyways. Forget about the 1600: you might as well light cigars with paper $$ you spend on this premium.
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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