How many cores do I realistically need to take advantage of Cinema’s capabilities less the need to render using Standard or Physical?

Hi Doc.  I’m running C4D R19 on a Mac Pro, but am seriously considering switching to a PC because I really want to take advantage of GPU rendering with Redshift.  Here’s my question.  Since I will be rendering with Redshift, how many cores do I realistically need to take advantage of Cinema’s capabilities less the need to render using Standard or Physical?  I’m considering the Intel Core i7 7820X 8 Core 3.6GHz, the Intel Core i7 6850K 6 Core 3.6GHz, the Intel Core i7 6900K 3.2 GHz 8 Core, and the Intel Core i9 7900X 3.3GHz 10 Core.  Thanks for your advice!

Mark