Minimum RTX 3060 12GB for iray rendering.
I used to have RTX 2060 6GB. What happened is on viewport the IRAY preview often looping for infinity, "Preparing Scenes" without spitting the result. Also, when rendering I often get black image, the process just stop after a view seconds.
The problem is because DAZ3D load everything first to VRAM. If your scene can't fit the VRAM. It will stop.
With RTX 2060 6GB sometimes it can process the scene at first, but for the second, third and so on times it will fail and demand closing and opening back the program. Somehow it can't flush the VRAM.
If you can get your hand on higher GPU with more CUDAs it will make your rendering process faster.
I choose RTX 3060 because its within my budget and I don't have to change my PSU 650W 80+ Bronze. Since the recommendation only require 550W PSU .