4 4 4 12 is faster, but it could also potentially be unstable if the RAM isn't rated for it, hence why some people would say 5 5 5 15 would be better. Looks like you have Crucial Ballistix, so it should be able to handle timings of 4 4 4 12 as long as the voltage is set correctly, which will either be 2.0 or 2.2V.