I've decided to take the advice of the wisemen and monitor through a Blackmagic Decklink Mini Monitor 4K card for my color grading display, which is a Benq SW240, calibrated with DisplayCal.
The Decklink card works with Vegas 17, and the color and gamma seem about the same as when monitored through the HDMI output on my graphics card. But there's a problem:
I noticed pretty quickly that the image coming from the Decklink looks slightly softer and less crisp than the image from the graphics card. It's subtle but unmistakable. A closer inspection shows that straight lines (like the edges of a building for example) are slightly pixelated, while through the graphics card those lines are sharp and clean.
I've tried changing a bunch of different settings both within Vegas and withini Blackmagic Desktop Video Setup, but nothing helped.
Anyone have any experience with this or good ideas? I realize it could be something wrong between Vegas and the Decklink card, but it could also be something wrong between the Decklink and the monitor.