Proofy :
CS:GO source can engine is only capable of using 2 cores so i3 6300 will perform amazing. Also if you take a proper motherboard such as ASRock B150/H170 Gaming K4/Hyper or MSI B150M bazooka and a decent speed DDR4 ram, you will be able to overclock i3 6300 easily on 4.4-4.5GHz
That would be an instance where saving money for the i3-6100 would be smart, as they are practically performing the same way anyway and overclock the same aswell (silicon lottery matter). Save 25 dollars and get a motherboard as good as the ASRock B150 Gaming/Hyper. You literally don't lose a fraction of performance. Also, you'll be able to run DDR4-2800+ memory, wouldn't miss out on it. 10+ fps difference in the latest open world games.