Greg Zaal, who runs HDRI Haven from Blender community has gone rogue and decide to release all his HDRI content for free from now on, you might consider supporting him on patreon but it's not required, no sign in or acknowledgments required. They're some of the best quality out there in various resolutions 1k to 16 K unclipped.
I've downloaded everything off his site and put some of them to the test below.