Dont know about sdcardreader on Pi4, but on 3B+ r/w-speed is about 23MB/s, if you want better performance use USB3 SSD.
If you spend $$ on faster SD cards you may be able to empirically measure a minor speed bump and it might boot marginally quicker, but in practical terms you will not notice any real-world difference in performance. Save goes for USB3 SSD drives; they are quicker in certain tests but you're unlikely to notice much difference (and you need to hang the drive out the back of the board, which is ugly).
If you spend $$ on faster SD cards you may be able to empirically measure a minor speed bump and it might boot marginally quicker, but in practical terms you will not notice any real-world difference in performance.
I currently don't know about SDCards, but some higher priced USB Stick (Sandisk Extreme Pro, the elder one's) do have TRIM, too.
USB Sticks and I guess sdcards too getting slow over time.
to reset to initial speed one need to full format (not "quick" under windows) them from time to time.
I guess a good measurement (not the card only, but Kernel, equipment, USB/SDCard) would be:
write speed:
dd if=/dev/zero of=tempfile bs=1MB count=10240
read speed:
dd if=tempfile of=/dev/zero bs=1MB count=10240
both with cd'ed to a folder on the USB/sdcard first !
anyway for an 256 GB Samsung EVO Plus (SAMSUNG MB-MC256HA-EU) under Windows/Linux with an sdcard reader (Transend TS-RDF5) I get this:
