Got SMB working, and I'm just streaming from the usb drive. 720p content is mostly fine, but 1080p is extremely slow. What's a fast drive to streaming smooth? I currently have this: https://www.amazon.com/Samsung-128GB-Flash-MUF-128BB-AM/dp/B017DH3O5A
Edit: Could it be format issues? I'm using SPMC on a Firestick and maybe it's transcoding?
I'm not sure it's your flash drive, the numbers don't make sense. What symptoms are you seeing?
Taking the absolute worst case, Netflix claims it can fit 4k video in a 25 mbit/sec channel. That's 3.1 MByte/sec.
Most flash drives I know of can read at 20-150 MByte/sec. You should be able to stream a handful of 4k videos from one flash drive, you should not be having trouble streaming one 1080p video.
Is it using USB 1.0? Do you have a lot of USB devices in a chain? Is it a very old drive? Slow computer?