I wonder if the M8 is the same panel, or a similar panel. I don't really need super high brightness, but if it suffers from VA's usual off-axis issues, that's a hard pass.
Anyhow, what I want is a 29-30" 5K panel. I have a 27" 5K iMac, and I find the screen is too small for 5K. The default font sizing is not ideal at my preferred seating distance. If I sit closer then I have more problems focusing on the screen.
4K 32" is not ideal for me either, since I would prefer more on-screen real estate in terms of actual resolution.
So, I'm currently using a 30" 2.5K Apple Cinema HD Display. IMO Apple nailed the non-Retina pixel density way back in 2004 at ~100 ppi, and an exact doubling/quadrupling of its resolution for "Retina" at ~200 ppi would be perfect. A 30" 5120x3200 Apple monitor would rock.