I leave this thread here if anyone else is searching in the future.
I was looking for some guidance before my most recent trip and I never found much on FT. I was wondering about the practicality of hopping from T8 to T4 and it seemed like the consensus was "not worth it" with less than 2 or 3 hours, but I must disagree.

I landed at gate-far-away 35 or something and had to hoof it through the underground tunnel to get to the main T8. That took all of 10 minutes. Then getting out of security to the airtrain took all of 10 more minutes. T4 is only 2 stops away. 5 min. I have Clear so getting through precheck at T4 was simple. The entire trip from gate to centurion lounge was 30 min. That was the hard part.

I thoroughly enjoyed the food and many fine beverages (get the espresso martini). It was definitely nicer than the AC. I spent about 90 min there.

The return trip was even easier. 6 minute train ride T4 to T8 and through precheck in 3 minutes at 15:00.

Is it a little bit of a hassle at JFK? Yes. Is it doable and worth it if you have ~2hrs to spare? Yes