You're not facing a resolution problem so much as a brightness and contrast problem.
Bright sunlight is about 120000 lux. That's about 38000 nits -- and the brightest specialty monitors I know of go up to about 10000 nits. A typical "wow, look at that" display is 2-3000 nits.
I do not want to downplay that we have a lot of improvement to do on contrast and brightness before we can match an actual window to the outdoors, but vegabook specifically called out his ability to resolve pixels on his 40-inch 4K. Resolution is still a problem. In fact, I feel we have a lot of improvement still to do in desktop displays and that resolution and size remain the most significant hurdles.
I run two of the Philips 40-inch 4Ks on my desk and although these are fantastic displays for the price, there are many areas for improvement.
Most importantly, and easiest to fix: they should be fully matte rather than semi-gloss. My contention is any display used for work should be matte unless you work in an environment with absolutely no lighting. Lighting glare is the most frustrating issue with computing, in large part because it's so easy to fix. In the early 2000s and before, monitors, including the highest-resolution monitors of the time, were almost exclusively matte. During the malignant era when living room displays converged into desktop workspaces and "HD" reigned terror on computing, we also accepted glossy/mirror displays. Although we have recovered from that period of resolution regression, matte remains marginalized.
40-inch at 4K is too small to use singularly and too low-resolution. I feel ideal is ~55 inches, concave, 10 to 15K horizontal resolution.
I think what's keeping us back as much as anything are video cards that can handle those displays. I have a 40" 4K as my primary desktop display, and run at native 1:1, it's still a little small for me. I often zoom websites to 125%. On that, I bought a GTX 1080, and it runs it well enough... native gaming really only works on older games and doesn't hit even 40fps consistently.
I have an i3-5010u as a backup, which has a 28" 4K attached... it feels sluggish just on desktop use (150% zoom) in windows.
I you want to push much more than that, you're going to need some really beefy video cards in tandum.
I'm a bit of a monitor nut myself and I too am running 2xBDM4065UC. Actually I run the second one above the first one, mounted at an angle towards me, and with a lean-back, headrested, programmers chair. It's awesome. If you can get used to the i3 tiling window manager, it's even better IMO, but that's a taste that not everybody acquires.
Maybe the new 43 inch version is more matte but I have not seen it yet. Could not agree more that a 55 inch'er 10k resolution, would be my absolutely perfect display. With a low radius curve, and possibly curved vertically too (i.e. a rectangular sector of a sphere) though I am not holding my breath for that.
>> I feel ideal is ~55 inches, concave, 10 to 15K horizontal resolution.
I'm with you on that. I run a pair of 27" 4Ks at native scaling, and I feel like I'm looking at a 10 year old monitor.
27" was about the smallest screen my eyes could tolerate at 1:1 scaling - I was driven by real estate more than sharpness. All other things being equal, I'd prefer a pair of 27" 8K monitors so that I can get my 4K equivalent real estate with crisper text.
I was all in on matte. Glossy screens were absolutely terrible in any kind of lighting... until the 2012 Retina MacBook Pro. Whatever reduced layer-gluing-this-to-that magic they did there reduced glare to the point where I just don't notice it anymore.
Meanwhile matte displays actually get more affected by light falling on them, just that it's spread out a bit.
Bright sunlight is about 120000 lux. That's about 38000 nits -- and the brightest specialty monitors I know of go up to about 10000 nits. A typical "wow, look at that" display is 2-3000 nits.