2x 4gb of ram or 1x 8gb?

2x4gb.

Reason being is that all modern ram is DOUBLE data rate, meaning that it takes both sticks to equal the 1600mhz speed.

Real world difference between 2x4gb and 1x8gb is 10-15% performance.

Also, you shouldnt buy single sticks, you should buy pairs.
When you buy a pair, that pair is made from the same sheet of silicone and is tested and garanteed by the factory to work together.
Even if you get the exact same speed, latency, timing, and even model; your two individualy purchased sticks could still be unstable together.
Thus it always best to purchase ram in kits.

Not quite ... Double Data rate means that DDR transfers data on both the rising and falling edges of the clock cycle... so when you see 800 in CPUz, you double it to get 1600

https://en.wikipedia.org/wiki/Double_data_rate

What we are talking about here us dual channel which means when you have a 'matched pair", the system will realize a speed increase ... in gaming, it's about 5% and can increase to 15% in sime applications.

RAM do not actually have to be purchased in matching pairs for them to work in dual channel mode. I have purchased and installed plenty of different RAM sticks from the same brand and even different brands (with the same timings) for laptops and desktops and never once did they not work in dual channel mode. However, it is best that both RAM sticks have the same capacity like two 4GB sticks. Using mixed pairs like a 4GB and 8GB stick of RAM together will still allow the RAM to operate in dual channel mode, but the transfer rate will be around 10% lower compared to using two 4GB RAM sticks or two 8GB RAM sticks.

As for 1x8GB or 2x4GB RAM configurations...

If your computer has a dedicated GPU, then it will have it's own RAM installed on the card so whether or not system RAM is operating in single or dual channel mode will not make a difference. There will be a difference in games, but it will be negligible.

If you are relying on integrated graphics, then it is best to get 2x4GB RAM sticks so that the RAM will be running in dual channel mode. The increase in data transfer rate will benefit the integrated graphic core and that can increase game performance by 5% to 15%; depending on the game.


The following article test games played using RAM in dual channel mode and single channel mode with a dedicated GPU. The conclusion is that in most of the games they tested, there was not significant performance gain when we enabled the dual-channel mode.

- The only game tested that showed a significant performance increase is Dying Light; 66 FPS in dual channel vs. 58 in single channel. A 13.8% gain for dual channel mode.

- However, Dragon Age: Inquisition performs slightly better in single channel mode; 116 FPS vs. 110 FPS. A 5.5% gain for single channel mode. Metal Gear Solid V also performed better in single channel mode; 48 FPS vs. 44 FPS. A 9.1% gain for single channel mode.



http://www.hardwaresecrets.com/does-dual-channel-memory-make-difference-in-gaming-performance/

the terms folks are struggling to remember are single channel memory access vs. dual channel.......

No one said that. What was said is that "RAM absolutely must be purchased in matching pairs for them to be guaranteed to work". If you have a 1 x 8GB stick installed and but another 8GB stick ... it may not work, I don't mean it may not work at double data rate, it may not work at all. And then the user is left with two sticks of incompatible RAM and no ability to return the product under warranty.... although you might get lucky at the store if returned within 30 days as many outlets have a no questions asked policy.

If you try an RMA after 30 days, you are not going be able to base a warranty claim based upon "I bought two separate packages of RAM and they don't work together" .... the manufacturer warrantees only that whatever comes in the package works together .... and that's why when you have a single stick fail in a matched pair that came in the same package, they send you 2 sticks not 1.

Your chances of getting it to work depend on several things:

1. The more things the same, the better. Make, Model, Speed, timings, module OEM, etc all factor in here, sometime counter intuitively. For example:

a) Many RAM vendors switch OEMs in the middle of a production run. Corsair's VP and Dominator line the performance level DDR3 used Hynix memory modules in the initial runs ... as production lines matured and yields improved, they decided to switched to a less expensive supplier. The used the same model number but the timings dropped from 10-12-12-28 to 10-12-12-31. As such, when getting that 2nd pair of RAM for your Corsair 10-12-12-28 VPs, you had a better chance of success buying Mushkin Redline w/ the identical Hynix 10-12-12-28 modules than the new Corsair VPs.

b) We had a user with RAM issues who wanted to upgrade back in the days of DDR2. He wanted to upgrade his set of Corsair 2 x 2 Gb to 4 x 2GB. My son was in a similar situation (Mushkin) so since I was looking, decided to grab 2 sets. Unfortunately neither Mushkin or Corsair were still making DDR2 and the only vendor available was GSkill w/ the same speed and timings. Adding the GSkill's to both boxes was a big fail. Before returning them, I tried the 4 Gskills together (two packages and it worked with a bit of a voltage tweak). On a lark, i tried the Mushkin w/ the Corsairs and they worked fine.

2. The 2nd issue is "just what are you asking for ?" With DDR3, as I said above, you have a pretty good shot. Yields on 1600 are obviously better than on 2400. So when "mixing pairs", the likelihood of a problem at 1600 is rather low ... however, the higher the performance, the harder it is to get a functioning matched pair. At 2400, you chances were about 50-50.