PS5 is not guaranteed to have SMT. 1.8x clockspeed is unrealistic(compared to Scorpio) that'd put it at 4.1 GHz, they're not even hitting that on 12nm+ 100+ watt desktops without overclocking/boost clocks. Mobile Ryzen runs at 2.0-2.5(high end) base currently. Who knows what it will end up in on console.
I meant with regard to the PS4, ~3GHz being my guess at an upper bound for 1.8x, 1.4 would be 2.2GHz. Seems like a reasonable range.
SMT is an insubstantial die area at this point and I don't see why they'd take it out. The 7th gen had SMT, didn't remove it for variable performance reasons. Likely a developer could toggle it on or off, but I see no reason to permanently remove the hardware, in x86 at least it's been pretty key at extracting more IPC out of wider designs.
Mobile Ryzen has Turbo Core and if cooling can provide, can run at clock speeds well higher than base, pretty consistently even in laptops if there's no GPU load, in a console it would have more cooling. A console designer would likely remove the variable nature of turbo core and reel in the top end while bringing up the bottom end while deciding on a stable clock. They can boost up to 3.8GHz, a console won't sustain that, but settling on 3GHz seems doable especially in another fab node shrink, just 500Mhz up from the current base clock while taking away boosts above it.
Even running a touch conservative on all areas, it seems this will be in the ballpark of 7-8G CPU changes. The very lowest tiers of Zen at the same clocks as Jaguar still offer nearly twice the IPC, and clock speed bumps compound the gains. I don't think Xenos - Jaguar even with so many more cores was in excess of a 4x gain in most areas (in paper Gflops it was a slight regression, but a game doesn't just do SIMD all day).
If your reference point is the XBO X, with its 31% Jaguar clock bump it ebbs away at some of the gain, but there's still a decent one to be had.