The key is the CAS Latency, (the first of the four timings) which is how long it takes to perform and action, lower is better, 10 for 1600 is slow, 9 is average. For 1600 a CL of 7 or 8 would be considered performance DRAM, As freq goes up each step so basically does the CL i.e. basic is 1600/9, then 1866/9-10 2133/10-11 are 'average' sets, performance is normally 1600/7 1866/8 2133/9 2400/10