I bought 32gb of 1600mhz RAM, Corsair Dominator - 1600 - 10-10-10-27 - 1.5V CMP32GX3M4X1600C10 to go with the following build. Some people mentioned that with the GPU's and CPU, I should have selected faster ram - Is there a better RAM I should have grabbed, ie. 1866 or 2133 and perhaps G.Skill Trident or Corsair dominator platinum?
The build is:
Motherboard: Asus Rampage IV Extreme
CPU: Intel i7-3930K 6-Core 3.2GHz Processor
Cooling: < NOTHING YET >
GPU: 2 SLI x SAPPHIRE Vapor-X 100351VXSR Radeon HD 7970 GHz Edition 3GB 384-bit GDDR5 PCI Express 3.0 x16 HDCP CrossFireX
RAM: Corsair Dominator 32GB (4x8GB) DDR3 1600 MHz (PC3 12800) (CMP32GX3M4X1600C10)
Hard-Drives: 2 x SAMSUNG 840 SSD Pro Series MZ-7PD256BW 2.5" 256GB SATA III MLC
Extra Space: WD VelociRaptor WD6000HLHX 600GB 10000 RPM SATA 6.0Gb/s 3.5"
Thermal Paste: Arctic Silver 5
PSU: Corsair HX 1050 1050W ATX12V / EPS12V SLI CrossFire Ready
Blu-Ray: ASUS Black Blu-ray Burner SATA BW-12B1ST/BLK/G/AS
Case: COOLER MASTER Storm Stryker SGC-5000W-KWN1 Black and White Steel ATX Full Tow
No you can overclock the CPU and the ram individually.
I have 1600MHz Vengeance cards which I have overclocked to 1866MHz and even 2000MHz and it ran without a problem. Dominator cards are far more overclockable than the vengeance cards.
To overclock I had to increase the voltage to get system stability. Now I'm currently running those cards at 1866MHz with the same timings and voltage 1.6v. All cards are being detected and running at triple channel.
Theoretically It is always better to get Higher frequency cards than to buy a lower frequency cards and overclock it. Since overclocking decreases the life of ram cards so it is not advisable to overclock, but since the real life of a ram card is hardly 4-5 years due to rapid advance in technology you don't need the extra life of the cards.