Since that is PoE powered I assume that means it is not reliant on WiFi for networking, which is great. I expect UI3 will run perfectly with a 1080p stream and you could even edit the streaming profile to increase the quality and bit rate since it is a little low by default. Something like 4000-8000 Kbps bit rate and quality 70 (in BI 6) or quality 50 (in BI 5) should give you a pristine image (keep i-frame interval at 1000).
If UI3 doesn't run well for some reason, you can change the H.264 player between JavaScript and HTML5 to see if one player works better than the other.
You can also edit the streaming profile you're using to reduce the frame rate, resolution, bit rate, etc. Something like 5 FPS is going to use a lot less resources than 30 FPS.
You even have the option of using a jpeg streaming profile, which will work on pretty much anything. You could fish up a laptop from 2005 and if you can get it to run a reasonably modern browser, you can probably get it to run UI3 in a Jpeg profile.
And for the very oldest devices, you can always
download UI2 which I expect would be able to run on an unpatched Windows XP machine using Internet Explorer.