3% of a 9900K, or a 10700K, on multi? Not hardly, is that some kind of bizarre napkin math you're doing?
These charts show big mult-thread gains of 10700K / 9900K vs 5600X - at stock.
If you want to run everything stock, these charts are a good representation.
However the only reason to buy a 10700K and not a 10700 is to overclock it, and the only reason to build your own in general is to tweak it.
I those cases both can perform far higher than these numbers - like 10-25% higher - using good air cooling or a relatively inexpensive AIO water cooler.
But on to the stock comparison -
From Guru3d :
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