I'm actually not as concerned as I initially was regarding getting native PS6 games on a 'PS6 Portable' and I genuinely think it'll be the case and it'll be mandated. Power draw doesn't scale down linearly for starters, so at ~1/15th power draw you should be able to get 1/6th to 1/5th the overall performance.
The GPU side can scale quite easily with resolution, frames & small fx tweaks. I was concerned about bandwidth, but if PS6 is making very efficient use of 640GB/s for 18-23TF RDNA5 (36-46 Dual-Issue), then I expect PS6P to make efficient use of the ~205GB/s for ~4TF RDNA5 (8 Dual-Issue); so there's a relative B/W per flop of 1.4-1.9x on the PS6P vs PS6...
Plus, there's the rumoured 16MB MALL/Infinity Cache for the PS6 Portable which hasn't been alluded to for the main PS6 console. So this offers not just an additional, relative bandwidth bump that with expectedly good cache hit rates puts you closer to an effective ~300GB/s overall and probably ~512GB/s for actual data in cache, it offers much-improved latency (about 1/8th I believe vs GDDR7 and 1/5th vs LPDDR5X) which in tandem with lower latency LP5X can allow the CPU a little more efficiency, not to mention vastly reduced power consumption for cache hits vs LP5X and especially G7.
Also, if the PS6 Portable has 4MB L2 on the GPU while the PS6 is in the 10-12MB range, then relative to the overall compute, that could give it another effective bandwidth, latency and power use/distribution advantage.
My one concern that remains somewhat is the CPU side. World simulation, complexity and the fundamental functionality of your game world which will be just as important in making lively next-gen games, may face some limitation.
But, let's say PS6 is using [for games] 8c/16t zen6c @ ~4.35GHz and PS6P is 4c/8t Zen6c @ ~3GHz, then you need to work with ~35% of the CPU throughput. The LP5X + MALL Cache latency advantage might give you a few percent bump in efficiency from less stalls, so let's say 38%. Significant downgrades in visual settings/complexity may get you down to around the 70% region from the initial load but if you're already batting up against the CPU limits on PS6 and pushing a complex/dense world simulation it may bottom out around there and not scale down anymore with visuals.
Cut from 60fps to 40fps gets you down to around 46%; then from there you can maybe par back some tick rates, complexity, density etc. on distant or objects less essential to gameplay without parring back the core experience too much. Perhaps Sony could allow for a small CPU<>GPU trade-off by devs as needed to clock up a bit. And then you should be in the ballpark. Or you could of course just take the hit and smash it right down to 30fps; and they've done that on Switch for many games, but I'd hope that for games where better response and reasonable clarity are required they'd try and aim for a nice middleground like 40fps. Of course a smaller display tends not to accentuate motion issues as much as big displays, but I still think 30fps is too low for specific games, 40 really does make a surprising difference.
The advantage of a handheld (or at least handheld modes) is you have a guaranteed specification on the display, so if they spec it with VRR+LFC then they don't have to adhere perfectly, allowing a little more slippage and can have modes in the region of ~40fps (or anywhere really) without having to worry whether you have a display to support it.
The one issue remains if you have a game only doing 30fps and maybe 40fps on PS6 with everything cranked and you're CPU-limited (think a GTA7 at the end of the gen [a little optimistic probably, lol]). Then what do you do on the portable? In some cases you might at best be able to trim back to the 50-60% region in terms of required throughput relative to the PS6 and you'd have a gulf to make up that can only be done by fundamentally limiting the core game functionality. You might just argue that devs have to make that decision and make those trade-offs, but it'd be a shame for this to significantly limit the scope of landmark titles that really try to push the boundaries. So for that reason I really hope that the final hardware is very favourable to the CPU side and every plausible optimisation is made and every dev-side option is entertained.
Some separate, rough examples for how PS6 Games could scale..
Eg. 1 (Advanced, more latency sensitive gameplay)
- PS6: ~1080p @ 60fps > 4x PSSR3/FSR5 > 2160p w/ Path Tracing
- PS6P: ~540p @ 40fps > 4x PSSR3/FSR5 > 1080p w/ RT GI + RT Reflections + reduced tick rate/complexity for distant view animations/physics & altered distant tri : pixel ratio/bias in virtual geometry.
Eg. 2 (Advanced, less latency sensitive gameplay)
- PS6: ~1080p @ 30/40fps > 4x PSSR3/FSR5 > 2160p w/ Comprehensive Path Tracing + Ultra-High Visuals
- PS6P: ~540p @ 30fps > 2x PSSR3/FSR5 > 720p > 2x HQ Spatial Upscale > 1080p w/ RT GI + RT Reflections + Med/High Visuals + reduced tick rate/complexity for distant view animations/physics, reduced density for non-essential distant simulated objects & altered distant tri : pixel ratio/bias in virtual geometry [CPU Priority Mode w/ CPU Clocks increased & GPU/Mem Clocks reduced].
Eg. 3 (Middleground)
- PS6: ~1440p @ 60fps > 2x PSSR3/FSR5 > 2160p w/ Higher Precision RT GI + RT Reflections/Shadows/AO
- PS6P: ~720p @ 40fps > 2x PSSR3/FSR5 > 1080p w/ Lower Precision RT GI + RT Reflections/AO + reduced tick rate/complexity for distant view animations/physics & reduced density for non-essential distant simulated objects.
Eg. 4 (Traditional)
- PS6: ~1800-2160p @ 30/40fps > PSSR3/FSR5 AA w/ Baked Lighting + RT Reflections/AO/Shadows
- PS6P: ~900-1080p @ 30fps/+ > PSSR3/FSR5 AA w/ Baked Lighting + RT Reflections/AO + reduced asset LoD distance.