Which current or recent gen GPU* would max out almost any game at 720P*/60fps while not being overkill?

*there is a good reason I will explain below

I am looking to upgrade a small ITX form factor server box that currently hosts Plex and a few other things, with the goal being to host my Steam library on this thing and run it headless with Sunshine/Moonlight as a game streaming server. With that in mind, the smaller and more efficient the better, hence recent gen, and the low resolution and framerate; it doesn't need to do anything more than that to stream gameplay for my preferences.