|"I have the mobo Asus M4A78-Pro, and it can support dual-channel RAM's and can have max 4 rams. I've already got two ram's installed, and will it cause problems to the system if i installed addiotional two rams(dual-channel)?"|
Insofar as you have not exceeded the maximum memory capacity of the motherboard, there should not be any problem. Just make sure that you purchase the correct memory. Ideally, you want to play it safe by purchasing sticks identical or similar to what you currently have. However, it is not mandatory for whatever modules you purchase to match your old ones for the sticks to work in dual channel mode; but, be sure you get something with the same speed as your current sticks.
"Another question tho. Is Intel Core I5 "just" as good as I7 to gaming or is I5 lower in performance?"
Core i7 is faster than the Core i5. But looking at the cost vs. performance benefit, Core i5 will get you the best bang for your buck.
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