I own a Sony A7RII 42 MP images are 7952px x 5304px what should be the best video card resolution for accurate post production? What could be the minimum acceptable?
If I understood the question correctly, the limitation is usually the monitor, not the video card. Any video card usually supports far higher resolutions than a typical monitor does.
As for me, I have three 1920x1200 screens (2.3 megapixels), and can perfectly well post-process 24 megapixel images. The key is that your photo editing software has a feature to zoom in. Use it!
You are unlikely to find a 42 megapixel monitor.
Instead, when choosing a monitor, focus on wide gamut, accurate calibrated color reproduction and 8-bit color (some monitors have 6-bit color and blink the pixels on and off to reproduce the extra 2 bits). You could also consider two monitors. A two-monitor setup allows you to have two full-screen applications open at the same time.
Any modern graphics card will support most modern monitors, and nearly any modern monitor will work fine for photo editing.
Screen resolution doesn't matter as much as the physical size of the monitor. Even then, it's not so much a hindrance to editing as it is a mere annoyance to scroll around the image. Also, monitors with high pixel densities, while good for viewing photos, are not necessarily better for editing, which sometimes requires zooming in for detail work. Something doable at 100% on a standard monitor at 96 dpi might require zooming in to 400% on a high-DPI monitor, where interpolation, pixel accuracy, and increased processing requirements may become a concern.
Color calibration can be an issue, but the main problem is usually figuring out how to do it, not whether it can be done. Most modern equipment can be adequately calibrated for photo editing.
Just get the video card and monitor that supports whatever games you like to play. They will work fine for editing.