Just a note about that, yes, CAS speeds matter, but, for General use, you honestly would never know the difference. We are talking milliseconds of time savings here. For certain long term number crunching apps you would see some time savings, but for average day to day use, as long as it seems ok stick with it.
The time saved you would lose later as you sipped your coffee.
I would stick with what you have, and just add more, or look to remove other bottlenecks in your system if you have any.
my 2cents