I always see people replied this way but is there any prove that you need more than 512MB VRAM when going over 20" LCD.
Back to those days, yeah, VRAM matters for bit depth and resolution. But since nowadays most GPU has at least 128MB or more, why it matters to have more than 512MB when going over 20"?

GPU job is to render image and send them to the monitor. Its the monitor responsibility to display it. GPU wont hold back the data unless you enable VSYNC. If your LCD unable to keep up with the GPU output, how can it be related to the GPU?

I dont think its off topic if its related to the monitor.

BTW, your assumption is wrong. First of all, GPU has ram too. Instead the hdd works like the monitor too. Receiving data from the CPU and the same can be said for the LCD receiving data from GPU. VRAM should come into question when it comes to resolution used and not the size of LCD being used.