I can barely see my text at 4k or UHD res much less 5k. Admittedly this may be a period of adjustment for me as I was really having a hard time with the 2560x1600 on a 30" when they first came out. I'm using it at UHD right now but anything more than that I cannot see the usability for myself personally. Curious to know what you guys do, apps you use if you do use it at native res or close to it. Also there is a setting for 6400x3600. What standard is that? I read something on Apple's community forums saying the 5K standard is rather obfuscated and that the 'best resolution' of 2560x1440' is actually 5K with pixel doubling or some such. Any idea?