I'm not sure why some people keep talking about "GTX 1080" performance. PS5 and Next XBox will use a much more efficient and advanced technology, which is not ready yet.
Teraflops alone means nothing. Furthermore, hardware in a close environment can produce far better results than the equivalent hardware into a PC.
People often talk about an equivalent PC to the consoles out at the time. It isn’t that it can produce better results, rather, it’s code can be honed in on as a result of the closed ecosystem. Furthermore, the tech in those consoles is very much ready and it will be customized and tailored to the devices. We’re not talking about machines that will be the most powerful things on the market.
What to watch for? Their CPUs and RAM (speed for the former, amount and speed for the latter).