I have a new eMac with 256 Mb built in memory. I'm thinking about getting a stick of 512 Mb to bump me up to 768 Mb. How much more speed will I get? I usually have a bunch of programs running at the same time, so I get the "spinning color thing" a lot. I play games too, and some games like Sim City 4 are sometimes really slow. Does it matter whether I get my memory from Crucial or Apple? Are they any difference when it comes to performance? Overall quality?