The 9900X3D has its 12 cores distributed equally on the two CCDs, which means that only 6 cores have access to the 3D v-cache. So when gaming, it behaves like a 6-core X3D CPU, while the two others have 8 cores running with the 3D cache. It's really not a big deal in most games, but if a title takes advantage of multi-core CPUs you gonna be penalized.
The 7950X3D is from a generation that still had the cache die on the top of the compute die, so AMD had to cripple its clock to prevent overheating. None of the 9000X3Ds has this problem since the cache die is now under the compute one.
The 9800X3D is without a doubt the best choice if you are mostly using the computer for gaming (and it's the less expensive of the three). It will use...