My friend wants to add more ram to his old PC, at the moment he has 4gb DDR2 crucial ram (1333mhz i guess not sure how to check it). Is it okay if he adds 4gb more (his old mobo supports up to 8gb) crucial ram with the same clock speed, I've heard its reccomended that the rams are all the same but the ram bundle what he has can't be found in estonia anymore.