The G3258 costs about 30% less and offers up to ~30% better performance than the FX-6300 when compared stock vs stock in popular RTS games like Supreme Commander 2, Strarcraft 2, etc. Most RTS games do not scale beyond 1-3 threads. When compared Overclocked vs overclocked, the G3258 will offer up to ~70% higher performance than the FX-6300 in many of those poorly threaded RTS games.
Core count and clock speed are not measures of execution resources or performance unless the comparison is of CPUs of the same architecture. Real-time workloads scale proportionally with core performance, they do not scale proportionally with core count, see Amdahls Law for an explanation of why.
The i3-4150 is priced more closely to the FX-6300 and is the best choice in that price class for gaming overall.