UPDATE:
So I recently moved Mydoco from the Pi 3B+ I was running it on to my Pi 4 8gb.
I spent some more time researching SD cards and bought one of these…
It’s the “V30” rating you need to look for.
This rating means the card is capable of a minimum of 30 MB/s write speeds, usually much higher. (They also have V60 and V90 rated cards that are even faster, but they are not cheap).
These cards are specifically designed for 4k and 8k ultra-high-def video recording on professional AV equipment. Thus they need to have very high throughput speeds.
Most SD cards and USB flash drives are advertised based on their read speeds. However, most of them have some horrendously slow write speeds (as I discovered after bench-marking all of my SD cards and USB flash drives)… but it is the write speeds that are much more important when using the card to run an operating system due to the constant high I/O throughput and random-access reads.
I actually bench-marked this V30 card on my desktop using Linux disk tools and a USB-3 card reader…
Read speeds were in excess of 300 MB/s.
More importantly, the write speeds were in excess of 80 MB/s.
Random access speeds were a mere 0.7 ms
All these specs WAY out-performed even a spinning hard drive connected with a USB-3 drive enclosure.
Since the Pi 4’s SD card reader is capable of the same speeds as a USB-3 port, it seems that this ultra-fast card is definitely making a very noticeable difference so far in how fast and smooth Mycodo now seems to be running on my Pi 4. I still haven’t enabled all of my Functions yet, but will be soon.
Ill post more updates as I continue testing.