Well, for video editing the important criteria for RAM is:
- Never, ever crashes - this is most important; choose only RAM vendor certified sticks (QVL certified) and don't use unmatched sticks
- Speed; faster is better - while true too, increases to RAM speed, or lowering of CAS wait cycles (latency) both contribute to speed but the gains are very slight; faster RAM is hardly noticable vs. faster CPU speed which is very noticable (I've played with this a lot on a couple of overclock builds and testing Premiere speed with PPBM and speeding up the CPU 5% helps performance about 5% where speeding up RAM about 30% helps speed about 1%)
Google "what is CAS for RAM" and speed a week self-teaching yourself if you want to even begin to really understand RAM! I know enough to know there is a lot to learn about the subject. The good news is you really don't need to know that much to build a reliable, great system for running Adobe products, including Premiere, Photoshop, and After Effects:
- Only use RAM that the memory vendor has certified for your motherboard; don't assume that if the vendor says a 4x8GB set of sticks that will work with your motherboard that two sets of said RAM will work with an 8-slot motherboard either! (too advanced to discuss here, but various factors can overload the memory controller in the cpu itself -- factors include RAM voltage, # of sticks, RAM clock speed, CAS wait state settings, cpu memory controller voltage, and possibly more)
- Increasing RAM speed helps ever so slightly for Premiere speed up to 1600 MHz (for x79 anyway) and RAM speed gains past that are even slighter
Now, getting back to why the two sets of sticks are the same cost. They very likely use the same RAM chips, which is a big factor for how much it costs to build the RAM sticks. While the Asus motherboard you are purchasing allows for complete customization of many, many, many things, unless you are an Extreme overclocker and planning to spend a few weeks tweaking a new build you simple go into the motherboard bios and tell it to use the XMP settings. This tells the motherboard how to set the RAM speed and CAS timings for your particular RAM sticks with the settings the vendor intended.
You really need to know a lot about what you are doing to safely set RAM timings in any other way than simply choosing XMP settings. And, you can easily toast your cpu if you don't know what you are doing and you choose some really bad settings.
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- Make up your mind about the number of memory sticks you want to install. On the X79 platform, do you want to use 4 slots, or do you want to fully populate all 8 slots? This is very important especially with i7-3930K / 4930K CPU's, which have a rather finicky memory controller.
- Make a shortlist of quad or octo packs of memory sticks in the size you want, limiting yourself to ONLY sticks using 1.5V or less.
- Check the motherboard manufacturer's site QVL list to see which of the sticks on your shortlist are approved. Pay attention to the number of slots for which they are approved. Some modules are approved for 4 slots only, others for fully populated use.
- Check the memory manufacturer's site QVL list to see which motherboards are approved.
- Try to establish if there are users that have been successful in using the sticks on your shortlist and delete any that were giving trouble to others. NewEgg can be a good source for that.
- Now that you have a very short shortlist, contact the Technical Support departments of both the motherboard manufacturer and the memory manufacturer and ask them to confirm or deny the compatibility of the memory modules in the quantity you need.
- If both confirm compatibility, check the physical height of the modules including heatsink in relation to the intended CPU cooler. Do they fit without modding?
In general, only buy matched sets of memory sticks. There are too many different sticks with the same type number, that will cause grief when bought as four single sticks, but you limit the risk by only buying quad sets or octo sets for fully populated X79 platforms.
CAS latency is no longer important, in fact, with the finicky nature of the memory controller of the Sandy Bridge-E, it can be advantageous to choose a higher CAS latency for improved compatibility. What can be important - relatively speaking, only in single digit % performance differences - is the rated speed of the memory, 1333 or 1600 or 2133 or even 2400.
Even though the X79 platform only supports - at least officially - up to DDR3-1600, one can use XMP profiles in the BIOS to have the memory run at its rated speed of say 2133. For my new 'Monster' I followed these steps and ended up with a fully populated 8 x 8GB octo set of G.Skill RipjawsZ F3 DDR3-2133 sticks that are running without any problems at 2180 MHz.
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You want bandwdith ie MHz speed up to 1600 first and ten CL rating after normally. The returns on speeds above 1600 so far have been neglible with the current applications.
Thanks for the detailed reply Jim! And cc and Eric. Much appreciated.