As you have surely discovered, options for a 4K monitor above 32" are very limited. Magnavox offers a 40" for about $899 that, because of some minor image instability issues, did not receive very positive reviews when it was released at the beginning of 2016. Newegg offers two discount brands that make a 40" monitor, namely Wasabi-Mango and Yamakasi. These do not appear to have positive customer feedback.
Newegg offers one model of 43" 4K display (which also supports 10-bit color.) This, again, is the Korean Wasabi-Mango. Positive feedback for this model included one new owner who said "anything from 720p to 2160p content ... looks amazing." Another measured actual power output as 61 to 66 watts. Another reviewer ditched his Roku3 and bought a Roku4 because as he said, "watching 4K content is fantastic on this monitor." This customer also hooked up a Raspberry Pi to it, and the setup worked just fine. At $769 the 43" Wasabi-Mango is not extremely cheap, but it isn't much more than what you would pay for a high quality 4K LED-TV.
A question often asked is: Should I just use a 4K flatscreen for my monitor?
The mainstream 43" 4K TVs at Newegg ranged in price from $379 (Visio/Hisense) to $649 (Sony/Samsung) which do function passably as PC monitors, but not optimally so, especially for graphic arts and photography where you need color calibration and image stability. My experience with using an LED-TV as a monitor is that the colors tend to be "bleedy" and somewhat hyper-realistic. You can have problems with ghosting and image jitter as well. As TVs, flatscreen LEDs are designed to display moving pictures and be viewed from a distance.
I could tentatively recommend the 43" Wasabi-Mango UHD430 at this time based on owner feedback, but it would probably be in your best interests to see what pans out after the holidays. This is going to be a hot market segment, and competition will push prices to more consumer-friendly levels by spring/summer 2017.
The formula for determining dot pitch on a 3840x2160 format is 4405/diagonal_size. So with your most standard 4K monitor size of 28" you'll have 4405/28" = 157 dpi. 43" monitors approach the ideal scaling ratio of 96 dpi: 4405/43 = 102 dpi. This is good size limit. It's hard to imagine how enormous a 43" screen is until you're actually sitting in front of it 18 inches away.