Using a 2015 5K iMac: 1. Is there a way in real time to check the transfer speeds of a Thunderbolt 2 device or a USB 3.1 device when transfer files? 2. The Apple website indicates that TB2 transfers at 20Gb/s and USB 3.1 transfers at 10Gb/s. Are these realistic speeds when using the proper cables? Should transfer rates always be around these speeds or does it change? 3. Besides price and the fact that there are more USB 3 devices, are there any reasons to use a USB3 cable vs. a TB2 if given the option? Thank you.