I really love this small openwrt router, but it gets pretty warm...
https://www.gl-inet.com/products/gl-ar750s/

So, i designed this thing, it is a bit "raw", to attach 120mm fan (i used Noctua), for cooling.
There is airflow from bottom and from side thru whole route.

I did run performance tests via wifi and Gigabit Ethernet, more than 1TB test transfers.
Sadly, not found benefit from cooling, no real performance advantage :(