Can 2 differnet ram cards be compatible with each other ie; G Skill and Kingston

Possibly, but do not count on it.
Ram is sold in kits for a reason.
A motherboard must manage all the ram using the same specs of voltage, cas and speed.
Ram from the same vendor and part number can be made up of differing manufacturing components over time.
Some motherboards can be very sensitive to this.
That is why ram vendors will NOT support ram that is not bought in one kit.
Although, I think the problem has lessened with the newer Intel chipsets. Still,
it is safer to get what you need in one kit.

If you must, buy the same speed, voltage and cas numbers.
 

Tradesman1

Legenda in Aeternum

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If they will play together they will run at what you can set them to run at, they generally go to the mobos default when mixed, then it's best to manually set them up (again if they play), you aren't locked into them running at the lowest speed of the two, that's long been a myth about DRAM, more on FAQs and Fiction about DRAM in my article here:

http://www.tomshardware.com/answers/id-2741495/ddr3-faqs-fiction.html