Well from what Ive heard people can max out games at 4k without an issue with haswell i5 and i7 since they have awesome single core perfomance.
Well most of games are GPU intensive rather than CPU.
And i disagree that there is little difference between old FX series and intel, there is a BIG one, single core perfomance which amd is a weakspot but its good at multitasking, even at ryzen its same thing.