The AMD Ryzen 7 9850X3D wins in 9 out of 14 comparable specs, with 2 ties. Its biggest advantage is L3 Cache (50% better).
Ryzen 9 3900X wins in 3 specs (Total Cores: 50% better).
Recommendation
Choose Ryzen 7 9850X3D if you want the best overall performance — especially l3 cache.
Choose Ryzen 9 3900X if total cores matters more to you.
