There are a few free apps that can measure read/write speeds of card/reader/cable easily. Change one, compare. I use:
"AJA System test lite" or "BlackMagicDisk Speed Test" (mac). Fast and effective way to see how fast the card and or reader is, or identify bad (or charge only) cables. You would be surprised how many usb cables are NOT capable of full transfer speeds, so I mark the ones that are in my bag. Also does a great job seeing how fast or slow external spinner or SSD drives are.
