If you work in the Adobe RGB colour space, it would be advantageous to have a monitor which has the best specification for that gamut. If you use sRGB colour gamut, go for one which has close to or more than 100% in that gamut. There are lots of really good IPS monitors out there now LG and Acer have 31.5 and 28 inch 4k monitors for around $300 U.S. and HP also makes good 4k monitors for that price. Dell monitors are also excellent. Since most cameras now give 24Mpx (6000x4000 px) images, a 4k screen is better suited for critical viewing as long as it is calibrated. If you have loads of dough, go for the professional screens. I invested in a colorimeter to ensure that my colours are calibrated, but I am very fussy about colour rendering. You say that you have done your research, so go to it! Enjoy.