so this would mean lower number for latency the better?
CAS Latency: Time between the CPU asking for data and RAM releasing it.
Technically, lower RAM timings are better (example: 8-8-8-21 is better than 9-9-9-24). However, with modern processors the performance increase isn't really worth the cost unless you absolutely must squeeze that last percentage point out of your system. Get the less expensive CL9 RAM and spend the extra on something that matters (for a gamer, that would be a better video card or processor).
Higher RAM speeds are better (example: 1600 is better than 1333). However, that's true only up to a point. Once you get up to 1866 or so, the timings have to be so loose (so much higher) that there's very little performance improvement.
Right now, I usually recommend 8GB of DDR3-1600 CL9 RAM for dual-channel systems. If you're getting triple-channel, then I recommend 6GB of DDR3-1600 CL9 as a minimum.