Gentlepersons…
I have 2x8Gb of DDR3 1866MHz RAM.
I’m thinking about getting another 16Gb.
And in that process, I wonder if I should just get another pair of the same spec I’ve got, or get a set of 4x8Gb DDR 2400MHz?
Would another 16Gb help in for instance, DCS?
Would there be a benefit in going from 1866 to 2400…?
I don’t think DCS or any other game ever came close to using my full 16GB. You can press CTRL - SHIFT - ESC and pull up the perfomance window to see how much RAM is being used. The highest I’ve really seen was in the high 12’s. There’s a big benefit in speed in that upgrade, but I don’t know if it’s worth the upgrade doing it now or holding off untill one day you adapt DDR4.
mixing different speeds MIGHT be possible. it depends on the timings, latency, CAS speed etcetera. It requires some research and the most likely, positive thing to happen is that the motherboard underclocks your new RAM to match the slowest RAM you got. Different RAM speeds may lead to stability issues.
Check that your MoBo supports 2400MHz to begin with.
LOL! No, it doesn’t…!
There are 2400 RAM in the qualified vendors list, but it turns out 1866 is the fastest the board can handle. I guess that means 2400 RAM can be used, but slowed down to 1866.
Anyway, thanks for making me look closer in the manual! 
Well, more than 16GB- I’m not even sure DCS address them at all…
As a Rule of Thumb I go for Suggested RAM for my best game…
Elite suggests 8GB. DCS too…
Double that if you have the dosh, but… 32 GB? Unless you have heavy graphics activities in mind (Editing, Photoshop) I’m afraid is wasted.
Yes there are ways to use RAM as HDD but…
To be honest I’ve found mixing old and new sticks, even of the same spec, is really hit or miss. I tried this when increasing my ram a couple years ago and it just wouldn’t boot properly until I removed the old sticks.
You’ll also want to check to see what max RAM your motherboard supports. Check forums, like those at overclocking.net, as opposed to the manual, as there might be a BIOS update or under-promise in the manual.
Got 32 Gig of DDR4 Memory in my rig. Should have stuck with 16Gb and used that money on something else. I never see more than 9GB used. That’s my experience.