Thanks for the opinions and references. I’ll do some more readings before deciding.
If someone is interested, the main candidates that I consider are:
4K sRGB: Viewsonic VP2780-4K - not so popular, but reviewed very favorably here for example, and fares well compared to higher spec-ed monitors.
More options: Dell P2715Q (quite cheap) and NEC EA275uhd-bk (quite expensive, compared here to the Viewsonic and others)
QHD sRGB: NEC EA275WMi - more calibration flexibility than the Viewsonic, at the expense of lower resolution
QHD Adobe RGB - Dell U2715h