Hi Emmette Coleman,
Thank you for reaching Microsoft Community. We appreciate for sharing your concern to us.
I am aware that you are interested in learning the read-write speed of the Surface Go 3's MicroSD drive.
The Surface Go 3 has a microSDXC port and supports microSD cards. This allows you to expand the capacity of storage available to you by up to about 2TB. According to our support article, Surface Go models have a microSD card slot capable of reading and writing SDXC cards with UHS-I read/write speeds. The speed would depend on the class of the card. The read and write speeds of the Surface Go 3’s microSD card slot are not specified. For more details, see What SD cards are compatible with my Surface? - Microsoft Support.
Kind regards,
Lavenia