Not sure if this will apply to anyone but I got my wireless performance greatly improved after months of trying out various tweaks. Connected to 5ghz, I would have a severe performance drops every few seconds in Steam Link. 2.4ghz was absolutely unplayable. Everything else network related seemed fine however.

I plugged it into an old TV and while running speedtest.net the video was cutting out during the whole run. I didn't have this at all on my newer TV. I tried switching the hdmi on the Pi from hdmi0 -> hdmi1 and it went away. I couldn't see Screen 1 (it was now only showing Screen 2) and had no Audio. Right out of the box it says if you use single monitor you must use hdmi0. I managed to boot up Steam Link and the network test showed no spikes or breaks, did some digging and found fixes for using hdmi1. Here are the steps:

1. Make sure everything is up to date. Apps, OS, RPI, etc. This helped but didn't solve it.

2. In /root/config.txt, make sure "hdmi_force_hotplug" is disabled by commenting it out. This will stop the Pi from outputting to two screens. If you bought it pre-installed or used NOOBS, it will likely be enabled.

3. Add this line to /root/cmdline.txt to get Audio out on hdmi1:
snd_bcm2835.enable_headphones=1 snd_bcm2835.enable_hdmi=1 snd_bcm2835.enable_compat_alsa=0

4. Shut down and switch the HDMI cable into hdmi1 (the one farthest from the power supply port).

5. Start it up.

Bonus: On my router I also switched the 5ghz channel to 165 as the higher channels are better able to go through objects apparently. Being on a different floor this boosted me from 20mpbs to 45mbps.