I think 4K 60 is a good bet, though perhaps it won't be rock-steady 60 fps throughout.
I was looking at Rage 2's X1X settings from Digital Foundry's video & decided to test on my V64 at 4K with them (1650mhz avg clocks, 1100mhz hbm2, ~310w chip).
I got around 45 fps in open world. Assuming proper parity with RX5700 as the chip that will be in the PS5, we can say that it will be somewhere around a 220w guzzling chip & yields ~56 fps on average, that's taking into account 1.25x performance over Vega & 1.5x efficiency.
Clearly, 220w (likely more) would be too much, but! There's room for tweaking when you're doing this with a custom design & games will be better optimised than Rage 2 for PC. In fact, if Navi adds VRS, it would only need a light touch of that setting to get you over the hump and towards 4K 60 as I can hold 60 fps with 80% resolution scaling and higher than X1X settings. If I could have lowered my voltage (card's locked) I could've had much better efficiency gains, so there's a lot more hope for PS5 on that front.
Even if 60 fps locked isn't in the cards for all games, with the addition of VRR this wouldn't matter as much, and either way, you'd get a WAY better experience across the board than what's possible on consoles right now in even the best scenario.
For what's likely going to cost £499, this will be a steal!