Every time I’ve tried to use it, I’ve either had to head downstairs to the PC to fix something or had terrible lag and artifacting making it unusable for even turn based games like Xcom…

That's not normal. While Steam Link is a bit older by now and as a result there are constrains like streamed resolution, your problems look more likely connected to your network than Steam Link itself. Digital Foundry talked about PlayStation Portal recently which also includes a two minutes chapter about best practices that apply to other game streaming devices as well: https://www.youtube.com/watch?v=jEoo_gbOBYo