Hi, i have the Geil 6400 ULL kit 2x512mb. I bought this because i didnt have enough to get the 2gb kit. now that i want to upgrade and get another 2x512 im a little worried because ive heard that having 4x512 isnt very good or can cause problems? can someone explain this to me and tell me whether or not its ok to get another 2x512 kit.