pic unrelated*

More than 8Gb is unnecessary for most people.

Unless it's bottlenecking your system I see no point.

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Based on AData's product list:
http://www.adata.com/en/xpg-dram/orderinfo/305

It looks like those two modules are the same speed with the same timings. They are likely the same underlying module with slightly different packaging (like a stylistically different heatsink).

If they are the same module, then you should be able to use them with each other without any kind of speed penalty. You will not want to spread the modules across channels, however - channel A should be matched DIMMs from the same kit, channel B should be the same. Mixing & matching RAM within the same channel is a recipe for pain.

Now, that being said, I don't see either of them on the QVL for your motherboard. I would post a link to the QVL except 7chan apparently doesn't like people posting links to active server pages, so I'd really rather not get banned again for trying to post innocuous technical information. If you type ASRock X99M Killer 3.1 QVL into Google the second result should be a link to ASRock's QVL page, which contains a link to your motherboard.

Basically your motherboard (and most motherboards, for that matter) are only guaranteed to work reliably with a list of modules that they've tested with that motherboard. If you want your system to work reliably then you buy modules off the QVL. If you want to take a chance then you can buy any module, but if you have trouble not even ASRock will help you resolve the issue.

Now, all that being said, I have two sets of 2400 modules in my PC that works fine so long as they're installed as individual pairs. They're on the QVL and are the same thing you're probably looking at here, the same module with different heatsinks. However when I install all four of them the motherboard won't POST if they're run at 2400. It will POST if I downclock them to 2300. For some added cushion I normally leave them at 2200 to avoid any chance of memory issues.

So QVLs exist and can be used to head off a lot of problems, however even then some combinations can be problematic and require additional effort.

>>22229
Thank you very much for the information. I will take my chances and go with mixing the AX4U2800W4G17-BRZ and the AX4U2800W4G17-DRZ. Surprisingly that ram cam prebuilt from Ibuypower.

>>22230
Not surprising, since ibuypower just buys the cheapest product they can find that meets the specs on paper and don't give a shit if it works or not.

They've shipped systems with holes punched through the motherboard.