Mixing different ram with same specs and brand

[CrimSoul]

so this is the ram I am currently using:
https://www.newegg.com/Product/Product.aspx?Item=N82E16820231460

Basically, I recently decided that I need to upgrade it as It just isn't enough. Sadly, I can't throw the money down at the moment for 2 more 4GB sticks, so I wanted to get just one for now. The problem is that this ram kit only comes in sets of 2 or 4.

I looked around and found this:
https://www.newegg.com/Product/Product.aspx?Item=N82E16820231720&cm_re=G.SKILL_Ripjaws_X_Series_4GB-_-20-231-720-_-Product

It's the same brand, has the same speed, CAS latency, timing, and voltage. Would it be safe to use this alongside the current ram instead?

 

[GhislainG]

It will be safe, but that 4GB module will run in single channel mode and you may run into compatibility issues. If I were you I'd get an identical kit (though there is no guarantee they'll be the same).

 

[kgt1182]

2x2GB RAM would give more RAM bandwidth then 1x4GB. If you are using an Intel CPU's or an AMD APU's integrated graphics you will see up to a 20% performance difference in gaming.

If you are using a external, discrete GPU card, the performance impact is very minimal, on the order of 0-5% at most for up to 4-core CPUs.

Single channel is okay unless you have 6 cores or more on the CPU aka i7 5820K or greater, then you want at least dual channel or the CPU will starve for bandwidth.