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Ya, your current Ram needs 1.65V to run at 1600 MHz speed. So do not buy a 1600 MHz Ram which operates at 1.5V.
Either sell of your old Rams and get three 4GB 1600 MHz CL9 1.5V modules (each will be around 2 to 2.2K) from Corsair or G-Skill or get the 3X2GB CORSAIR DOMINATOR 6GB (3 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model CMP6GX3M3A1600C8 - Newegg.com
Either sell of your old Rams and get three 4GB 1600 MHz CL9 1.5V modules (each will be around 2 to 2.2K) from Corsair or G-Skill or get the 3X2GB CORSAIR DOMINATOR 6GB (3 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model CMP6GX3M3A1600C8 - Newegg.com