Tips on upgrading 2013 Mac Pro processor for Nuendo use.

Warning, this message contains no quantitative answers.

Your question sounds like the classic “faster processor with fewer cores or slower processor with more cores”.
You may know this - multithreading is not perfect - double the cores, you don’t get double the performance, not even close. The basic multithread implementation requires some overhead plus applications can only multithread to a certain degree. Some applications are not suited to it, audio apps are to a degree.

The Xeons you reference all have similar characteristics within their specifications. The MacOS does a reasonably good job of multithreading. The Nuendo/Cubase multithread allocation is not great but exists. In my opinion Steinberg has optimized the multithreading slightly more on Windows but the last time I compared was several versions ago.

Nothing in the physical architecture of the nMP slows that down.

Conclusion of all this - there are a bunch of Windows-centric sites that do the very comparison you want. I forgot their names, some include DAW in the site’s name, but they are dedicated to doing DAW comparisons on just about every Windows platform you can imagine. If you find some of the reputable ones you can get some core vs. speed comparisons.