Besides the usual disclosed 4-4-4-12 or 5-5-5-15 timings there are sub-timings in the SPD. This low latency part's sub timings have been tweaked for maximum performance for Mac. So I can assure you our CAS4 RAM will differ in performance from others CAS4 RAM. Also some memory may pass standard memory test like Memtest86 and RST Pro but we have found that it may fail Apple's Memory Validation Test. That is why we have standard RAM and Apple specific RAM.