Very fastest way to serve files

I want a device on my network that would enable me to serve files at the VERY BEST speed.
This device would have say up to 1tb of capacity, but could be less than 250gb.

I have UNRAID Plus running Version 6.1.9.
I really like UNRAID and have been running in for more than 5 years now. Very happy.
In Writing to UNRAID the speed is not mind blowing. And that is perfectly fine.
I use UNRAID mostly as a media file server for my Home entertainment. Also for my documents and photo’s.
I only have 4 slots on my UNRAID mobo, all used up. (parity +3). I don’t want to mess around with Cache drives and adding one will mean purchasing more hardware to accomodate it.

I am considering the following course of action:
Retain all my older movies, shows, documents on UNRAID.
Employ a new device/system to store most Recent / Current files
Periodically copy this category of files to my UNRAID

The upshot would be that UNRAID acts as my secure data storage backup and “older media files” server.
Whilst the other ‘system’ would receive and serve the newest files at maximum possible speed.

Setup:
I have an ONHUB router running wireless AC.
Wired connection to 5 port TPlink switch
Wired connection to UNRAID
Philips Hue + Smartthings Hub
All other devices are wirelessly connected to the router
My devices are 3 windows PC’s
2 Nexus players
1 Nvidia Shield Media player

Question:
How should i serve files the very fastest ?
Should I get a device to attach to the router via USB ?
What is best ?

Thanks.