GL-AR750S Slate SMB xfer speed

I just received my slate and am experimenting with SMB access from a Macbook.
I have no problem reading/writing to the microSD card, but my transfer rates seem low; perhaps 2-5MB/s. Is this typical? Any thoughts on how to speed it up?
I am using a high speed MicroSD card.
Would attaching a USB drive be faster?

The speed is related with SD card model, and filesystem type.

You can formatting it to ext4 or change another microSD.