I am no expert on this but from what I read on Daz forum that Iray does not support any memory pooling (probably on purpose by Nvidia so they don't erode the 20x premium on professional cards). So it's kind of like RAID where your max VRAM capacity is the smallest of the combo. In 2x8GB, Iray only sees 8GB but you still get the benefit of 2xGPU rendering speed.So what if you have 2 GPUs with 8GB each? Will you be able to use both the GPUs (so 16GB total memory) or it doesn't matter?