hello guys , just to let you know i bought 2 ram sticks 4gb 1333mhz each and tried them on my macbook white 6.1 with 2gb ram 1066mhz , i was scared because what if they don't work , or what if one of the sticks burns my mainboard or something , well , nothing of that happened and my happy because it supported de 8gb 1333mhz ! here are the profs :

so if you have a macbook white with the useless 2gb ram sticks i hardly recommend to upgrade to 8gb , it runs amazing ! worth it