Thanks to all who have responded to my post. WOW! A lot of good information and links. I now know more about SD cards than I really wanted to
My 3 - 16 GB Sandisk cards are marked A1. They provided good performance. My 3 - 16 GB PNY brand are not so marked but they work OK. That said, the biggest problem I have with the Raspberry Pi computer is that it finds its way into a "production" use before I have enough play time
My original Pi 3B became the gateway, firewall, router, VPN sharing box for my LAN. It replaced a small Intel based PC.
So I purchased a 3B+ as a toy. Before long it was dedicated as a BitTorrent client. It has a 240 GB Crucial M500 SSD connected with a StarTech USB to SATA adapter cable. (I have a couple of those adapters. They work great but the Pi still boots from the MicroSD card).
And I purchased another 3B+ which last weekend it became the jukebox for my workshop. It is attached with Velcro to the back of an old 15" LCD monitor. It has a dongle for a wireless mouse and a 32 GB flash drive with my 450+ album music collection converted to mp3 files. A low privilege user account automatically logs on, starts Caja pointing to the flash drive and the Audacious music player. I can navigate it with the mouse alone, no keyboard required.
And I purchased another 3B+. So far this one has escaped being assigned to a permanent job
All of my "production" Pi's are running in "server" roles. Once they are booted they tend to stay up unless I take them down for maintenance or similar. They do not need to do much IO to the MicroSD card so the card speed is not a concern. My "play" Pi is running from one of the A1 Sandisk cards so I guess I have optimized the usage of my "best" cards.
I think my newest Pi is safe for a while. Last evening my neighbor brought over literally a pickup truck load of OLD PCs which his boss had told him to get rid of! My neighbor wants to learn about Linux and I told him I would go through the junk pile and see what might be useful to set up a little training environment. Talk about old crap - I threw away newer items 10 years ago. I did find a Core2 Duo based machine which seems to run Ubuntu rather well. Now if I can find another machine to configure as a play server... Anyone want some scrap metal? Free for the pickup. Perhaps I should give the Smithsonian museum a call
p.s. Sandisk customer service determined that the troublesome 64 GB MicroSD card which stated all this was a counterfeit. Ebay refunded my money and I have reported the phony item to them. I do not know if the seller was intentionally selling these things or if they had gotten into the supply chain before he got a hold of them.