i have a sapphire 6870 1gb http://www.newegg.com/Product/Product.aspx?Item=N82E16814102925 ... and im trying to crossfire it with a xfx 6870 2gb card ..http://www.newegg.com/Product/Product.aspx?Item=N82E16814150563 will this cause any instability?? with different amount of memory or will it just crossfire with 3gb of memory?? anyone please enlighten me if i should make this purchase.