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Using DDR4-2666 RAM with same brand DDR4-2400 ?

Ibn Saeed

Dec 2, 2007
Hello My specs are :

Motherboard Model: ASRock X99 Extreme6

Processor Name: Intel Core i7-5820K

Video Chipset: NVIDIA GeForce GTX 750 Ti


My question is regarding :

Corsair Vengeance LPX 16GB **DDR4-2400** PC4-19200

Corsair Vengeance LPX 16GB **DDR4-2666** PC4-21300

I have a build with the following ram DDR4-2400 :

Corsair Vengeance LPX 16GB DDR4-2400

and i want to add another 16GB

i am getting DDR4-2666 at a cheaper price:

Corsair Vengeance LPX 16GB DDR4-2666

Is it advisable to use ram from same brand, size but different speed ?

Would it cause any issues ?
Last edited:


Elite Member
Super Moderator
May 4, 2000
X99 motherboards seem to be finicky with RAM to begin with, so it's not advisable to do that.

It's always best to use the exact same RAM, and not mix different types of modules. You can try it out if you are feeling adventurous, as the best case scenario will be it works, and all the RAM will simply work at the speed of the slowest module. The worst case scenario is your system might not boot, or you could experience instability and crashes.


Golden Member
Aug 26, 2014
Yeah, +1 on that.

Absolutely best case scenario, your 2400 RAM can OC to match your 2666, and the motherboard/CPU/memory controller are able to run at those speeds. This is highly unlikely.

Most likely, you'd have to underclock your faster RAM. But even this might not work. Go for matched sets whenever possible. Underclocking should be fine, but there are no guarantees.