ChipFlip
Threadripper comes in two lines and the naming does a poor job of explaining the difference. The Ryzen Threadripper 9970X runs $1,699.99 used. The Threadripper PRO 7965WX runs $1,614.99. Eighty-five dollars apart, one generation apart, and aimed at different machines.
PRO is not a tier, it's a platform
The WX chips are the workstation line: more PCIe lanes, eight memory channels instead of four, registered ECC memory support, and manageability features. They need a WRX motherboard. The non-PRO X chips run on TRX boards with fewer lanes and fewer memory channels.
That distinction decides the build before performance enters the conversation. Buying the wrong one means buying the wrong motherboard too, and Threadripper boards are not cheap.
Generation versus lane count
The 9970X is newer silicon with better per-core performance and efficiency. The 7965WX is older but has the platform advantages above.
If your workload is compile times, rendering, or anything that scales across cores without needing enormous I/O, the newer non-PRO chip is the better buy. If you're attaching multiple GPUs, high-speed capture cards, and several NVMe drives at once, lane count stops being a specification and becomes a hard limit.
Check the board before the chip
This is the part people get wrong. A Threadripper CPU without a matching board is an expensive paperweight, and used WRX boards carry their own premium. Price the platform, not the processor.
ECC support matters too if the machine does work where a silent memory error is expensive.
Bottom line
For compute-heavy work with normal I/O needs, take the 9970X. It's newer and faster per core for $85 more. For a workstation that needs lanes, memory channels, or ECC, the 7965WX is the only one of these two that can do the job, and the generation gap is a fair trade.