I tried the shadow resolution at 8kx8k but it looks fake, although precise in other uses, but just fake looking on character models.
4kx4k works really well. And as said 16x is for multiple GPUs, or dual GPU cards, 16x will work on a single GPU but it will push it very hard to the point of burning it.
Hey Dab, what cpu/gpu/monitor setup are you playing on these days?