The iMac19,2 models use 8th Gen Intel Core CPUs, whereas iMac19,1 uses 9th Gen - just like your system.
Pls double-check that claim...
I AM WRONG, OP IS RIGHT
I missed a BTO 19,1 "Core i9" with 9900K...
Technical specifications for the iMac "Core i9" 3.6 27" (5K, 2019). Dates sold, processor type, memory info, hard drive details, price and more.
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My orig points can somewhat still hobble along, barely standing...
The following previous comment is true, except for the BTO mentioned above—
Based on Everymac the 19,1 and 19,2 are both 8th gen, Radeon Pro 500 series, 4K and 5K respectively.
I don't think Apple ever mixed generations within a system ID (eg, 19,1) but even if they did it would odd for a later generation to appear in earlier ID.
Clearly they did — per above link, so I was just wrong.
However, what does this mean for SMBIOS when 19,1 vs 19,2?
Take OP's point at face value that an 19,1 SMBIOS accounts for 9th gen 8-cores in a way that 19,2 doesn't.
Note on power:
By virtue of 9900K being unlocked, but thermal limitations of iMac case given a Radeon Pro 580X which can hit 180W, Apple's vectors may allow turbo SCore but cap MC freq below thermal max of 9900K? I can only guess, but case sensors may inform power provide a stepwise reduction in MC freq under full load? So it benchmarks well and degrades gracefully. Pure handwaving but this could be a build where you want to create your own power vectors for max perf, assuming you've thought through cooling.
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Technical specifications for the iMac "Core i5" 3.0 27" (5K, 2019). Dates sold, processor type, memory info, hard drive details, price and more.
Technical specifications for the iMac "Core i7" 3.2 21.5" (4K, 2019). Dates sold, processor type, memory info, hard drive details, price and more.
(It's not perfectly clear from the specs but I think both include Intel UHD graphics, IOW they are not F chips, so these are suitable for a mixed GPU build if that matters to you, meaning you can run your display without a dGPU or connect display to a dGPU and have iGPU also up available to VideoToolBox as co-processor).
I am far from an expert, but here are my rules of thumb...
Choosing SMBIOS I think about harmonizing the choice in following priority:
- macOS version,
- Desktop / laptop,
- Intel Generation,
- dGPU only, iGPU only, or both.
Overall, hitting SMBIOS on the nose makes a build easier, but it's not a showstopper. You can fake CPUID to account for generations and cores, write your own power vectors, tailor display connectors for iGPU-only unusual ports, tailor ACPI for sleep, networking/TB etc. But whatever you choose it needs to fit within overall era of macOS where you want to avoid older macOS on newer HW.