I think command rate is the time taken for the memory to go over the data being read; so it's counted as a cycle. For example, 1T would be where the memory will go over the data in every cycle, whereas 2T would be going over the data every other cycle. 1T should be slightly higher performance over 2T, but it's probably not that important in every day tasks (browsing, entertainment, documents). It would be heavily aimed for those who are doing heavy duty benchmarking or trying to earn a world record. Please correct me if I'm wrong though, as this is what I've overheard a long time ago.