It doesn't affect the quality. A CAS of 6 is still a good speed rating. The lower the better though. Typically, you don't find much below 4 anymore though. So, in real world terms, how much difference will the average user notice?! None. Even hardcore gaming wouldn't be affected much. But, having more memory will affect the amount of data that can be processed, so it will be more important to have more GBs than to have a lower CAS. Good luck.