Bits is bits. They are either there "1" or absent "0" -- if the existing cable does not "lose" bits, then no amount of cable improvement will make any sonic difference. Period.
I'm not sure if there are any cable eval tools. One way to do it would be to hang a large disk drive off your USB and test cable and turn on disk driver debugging (using some sort of Linux) to see if there are any read/write errors, then pump data to it all day long. A 6MB/sec disk or SSD would be the best.