Can i use my G.Skill x series ram with other different branded ram that i scrapped from an old premade rig?
Well sure, but make sure it has the same memory speeds or you could get BSOD and other terrible, terrible things.
You can but keep in mind if the memory speeds, timings and voltages are different, the system will auto set some strange settings and low speeds if one of the sticks is much slower. You can correct them with proper tuning in the bios to fix it, but be careful :)
Example would be if I threw in one DDR3 1600MHz 9-9-9-28 and one 1333MHz 11-11-11-29, the system would set your overall speeds to something like 1333MHz with timings like 9-11-11-28 and that could cause massive performance issues and possibly hardware glichtes.
you can do it, but if timings, speeds and voltages are totaly diffrent, then i would not recommend it.
Because you can run into serious headaces if you mix arround with that.