In real world terms it takes an overclocked Phenom II X4 or FX-6300/6350 to compete/beat an Intel 13 dual core with hyper threading that does not overclock.
For gaming the I5 (2500K, 3570K, 4670K) outperforms AMD
4670K is 22nm 84 watt (with HD4600 graphics) 1.4/1.6 Billion transistors depending on count metodology
Phenom II X4 965 is 125/140 watt, no graphics, 45nm, 748 million transistors
FX-8350 125+ watt, no graphics, 32 nm, 1.2 Billion transistors
Anyway the Phenom II x4 is 4 cores, the FX-8350 is 4 module/8 core, some programs can use all 8 core, some only 4, some one or two.
Most games give the 4670K/3570K 35 TO 70% advantage to Intel, 4670K $240, FX-8350 $180-200.
Generally, with a few specific game exceptions, real world gamers do not notice a performance difference. Overclockers like the FX ability to reach 4.4-5+ GHz given adequate cooling, motherboard and RAM. Intel absolute overclocks have decreased with each die shrink, but so has power consumption (though Haswell VRM control on die and increased graphic performance sort of minimizes Ivy Bridge to Haswell "jump."
Intel also has enough market share software is taking advantage of hyperthreading more than AMDs 1 module/ 2 core design.
Phenom II x4 overclocked remains a good gaming chip, though 6 core are preferred. FX Chips are one die with functions removed, ie 8350>8320>6350>4350. Mostly? 8320 can overclock to 8350 levels. 63xx and 43xx are 95 watt, there are 83xx 95 watt variants.