Thanks Joe and Ira. I'm seriously rethinking a TB drive in favor of 7200 rpm and USB 3. I'll be using the external drives strictly for backup, one for Time Machine and the other as a clone. My main concern was the speed of data transfer in case I either had to restore from TM or run the computer from the clone. I have been spoiled by my present Mac Pro because all the drives are internal. The new Mac Pro doesn't have that option and it's way overpriced for my needs.

When I have made a final decision, I'll post it. I'm glad that I haven't rushed into anything.

Jon

macOS 11.7.10, iMac Retina 5K 27-inch, late 2014, 3.5 GHz Intel Core i5, 1 TB fusion drive, 16 GB RAM, Epson SureColor P600, Photoshop CC, Lightroom CC, MS Office 365