DDR4-RAM CAS Selection Question

[Guest]

I am currently researching DDR4 RAM for the rebuild of my gaming PC. I know that I would like to have 16 GB of RAM using two 8 GB sticks and match the 2400 MHz max memory speed of the Kaby Lake i5-7600K or i7-7700K. However, I am uncertain about the CAS or latency speed I should go with. On PCPartPicker, the CAS for the RAM sticks that I am considering is between 10 and 16. I was told that CAS 16 would be plenty fast for gaming, but I just want to make sure before I finalize my pick and make the purchase. Is CAS 16 plenty fast for gaming or should I go with a lower CAS latency? Thanks.

 

[Zerk2012]

If your using a Z270 board then you can buy faster memory and make it work at that speed you should at the least be able to simply enable XMP profile and get 2800 to work. Lower CAS the better.
I would probably go with one of these with a Z270 board. Might be as simple as enabling XMP or could need just a bit of tweaking.
http://pcpartpicker.com/products/compare/V78H99,L2mxFT,p2mxFT/

 

[Multipack]

The higher the frequency, the higher the CAS because of the relay lengths, but CAS is pretty much the same on all DDR4 chips and it's far less relevant than it was with DDR3. DDR3 may have 1/3 lower latency than a 3800MHz DDR4 module, but do you really think it's slower? Of course not.

Because of the L3 cache is Skylake/KabyLake and the IMC being included in the chip there's no need for such latency with RAM these days. CAS 16 is plenty, and 2400MHz is still pretty low by today's standards and officially supported on Kaby (unlike Skylake).

 

[Guest]

I have one other question that just popped in my head. When I built my first gaming PC three years ago, my intel i5-4670K supported memory speeds of 1333 and 1600 MHz. I bought DDR3 RAM sticks that had 1600 MHz speed. With the i7-7700K that I am considering, it supports DDR4 memory speeds of 2133 and 2400 MHz. I originally thought that the memory speeds mentioned on the specs of both the CPU and RAM were the same thing and bought RAM with the memory speed that matched the max factory memory speed of the CPU. Did I interpret the specs correctly or incorrectly? I am not planning to overclock at this time, but I want to be able to get the max factory memory speed out of both the RAM and CPU.

 

[Multipack]

You dont need to match frequency with the CPU spec. Official support is always very conservative. Officially Skylake only supported 2133MHz but XMP allowed people to use RAM up to close to 4000MHz with a z170 board, and although Intel upped official support to 2400MHz with Kaby Lake I have seen z270 boards support 4200MHz RAM. All of them run at 2133MHz unless XMP is enabled in BIOS though.

With a 7700k I'd be looking at getting a little higher than 2400MHz. It doesn't make a huge difference, but it doesnt hurt either. Around 3000MHz would be the sweet spot imo.

 

[Guest]

I am looking at Corsair Vengeance LPX 16 GB (2 x 8) sticks with CAS 15 and DDR4-3200. Would this be a good choice of RAM for gaming?

 

[Multipack]

Pretty much ideal. I have the LPX 3000MHz and they have given me zero problems for around a year now. They are basically the same as Dominator Platz without the fancy heatsinks and LEDs, and 3200MHz will be just right.