Outsource streaming to 2 out of 6 cores?

Moin, I stream in my free time Fortnite. To maximize performance while playing, I thought I could stream out to core 5 and 6 of my i7 8700k (5.0 Ghz) and fortnite to 1-4. (since fortnite used only 4 cores anyway?) Question 1, is that so that it uses only 4 cores and ask two, if so, does that make any sense to split it that way or does the computer by itself do that well enough?

Just try it out.

Will I, nevertheless, I attach importance to the opinion of possibly wise people who have more information than I could ever find out with my rumgeteste. And to clarify would be even if Fortnite really only 4 cores used or not.

There are the Task Manager or you use a program that shows you that.