iMac 5k 27 2019 sd card reader speed issue

I have an iMac 5k 27 2019 on macOS Catalina 10.15.6

My SD card is SanDisk Extreme Pro SDHC/SDXC UHS-I Card 256GB [R:170 W:90]

I am moving multiple videos from multiple SD cards to my iMac every day for further processing. Each card has one mov file which is about 200GB. I am having trouble getting this SD card read speed to 170MB/s. I tried using Blackmagic speed test app to test my SD card and the result is capped at about 80-90MB/s read/write speed. Practical experience agree with that. Do I need to purchase a special SD card reader to achieve the rated read speed of 170MB/s? Is the built in SD card reader from iMac capped at 90MB/s? The system report shows my card reader has Link Speed 2.5GT/s, but I don't understand the equivalent MB/s of that. Thank you.