overclocking the fx 6300 will cost you more electricity, but that is negligible. problems should not occur.
well, the "raw performance" of the fx 6300 is comparable to an i3 6100 while being about 20% cheaper. if you overclock the fx 6300, it becomes an even better option. additionally directx 12 might eliminate the need to upgrade
the fact that he considers a fx 6300 means his budget is really low. while i agree that a ddr4 plattform with an h170 board would give the option to upgrade to an i5 6600, it costs more. therefore he would probably cut the budget of the GPU which is never a good choice today, as pretty much all games run into GPU limits (besides COH 2, which doesnt run at all
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but this discussion is senseless without knowing what the OP currently has (maybe some ddr3 sticks) and what his budget is
Overclocking "costs" you in terms of mainboard and cooling - people seem to forget about that quite often.
While the FX is a decent CPU overall, it's outdated and severely lacks single-threaded performance - which he needs for a lot of games on the market right now, including COH2. While at the same time there's no upgrade path with the AM3 socket, nor decent performance to begin with.
"Costs more" is a matter of calculation. Buy cheap, buy twice.
Personally i really can't recommend AMD CPUs for any gaming system right now. Zen might change that again, and GPUs are certainly a good alternative.
Anyways, half the topic is our argueing anyways. Truth is somewhere in the middle, i guess we can agree on that.