Actually airflow through the case and data corruption are the two main purchasing plus's, its conductors are basically copper wire, one will not transfer any faster than the other, the biggest advantage of round cables is not restricting the airflow through the case like flat ribbon cables do, and properly shielded round cables have virtually 0% data loss, some of the best round cables I've seen and the type I use are the Antec cables, they're not only twisted and shielded they have an included grounding wire that runs through the cable that grounds to the case.
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