You do a core scaling benchmark and find out for yourself since there aren't many of those on the web.
Set resolution to 720p or lower
Do a benchmark run then disable a core then do the same benchmark run and so on until you run it on a single core
Note your Avg FPS and see how well it scales.
A few examples from my tests:
Dota 2 and Source Engine games like Portal / TF2 / CS:GO etc (old engine) Max 3 cores - 1 core always overused A.K.A main core
Dota 2 (new engine - 4 (or more?) cores / more balanced load
Crysis 3 - 6-8 cores - heavy load on the first 6
Witcher 3 - initial patch i was getting 4 cores max but after that things improved to more (?) cores