It really depend on your Excel's calculation and formula that determine how many CPU/Thread the excel utilise.
I do a lot of work on Excel and do create financial models for my work. On a daily basis, my model do calculation where 4 columns with formula independent of each, and with 20k+ rows of data, crosses to different tab with 100k+ rows of data to bring back information. When it is calculating, I can see the Excel Status bar indicates 4 threads in use, and takes approximately 3-5mins to calculate.
I know this hasn't give the answer that the OP wants, but like other said, you will need to review your excel's formulas and see how that calculate/flow of data before determine the type of CPU needed.