While not dependent, the question, to return to your analogy, is rather, "Can I get from South Africa to Japan in 12 hours?" Obviously if you take a scheduled bus that only runs every 4 hours, and you lose 4 hours waiting for it, it's going to "eat up" time that would otherwise be available for the air trip, and would make it that much harder to meet your deadline. Similarly, if your goal is to make "best use of" a high transfer speed within the disk (from the platters to the buffers), having a slow interface can become a bottleneck, much like waiting for the bus for 4 hours. — allquixotic 21 secs ago