The FX6 series have three computing modules, the FX 8 series have four computing modules. For gaming, an overclocked FX 6 is about the same as an equivalent FX 8 at the same clock speed because all of the modules are not being used.
In your cost analysis, you must consider more than just the CPU.
These are German prices.
This is what it takes to run an i5 4460
PCPartPicker part list /
Price breakdown by merchant
CPU: Intel Core i5-4460 3.2GHz Quad-Core Processor (€182.94 @ Amazon Deutschland)
Motherboard: ASRock H97M PRO4 Micro ATX LGA1150 Motherboard (€87.84 @ Mindfactory)
Total: €270.78
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-09-21 11:21 CEST+0200
For an overclocked FX 6
PCPartPicker part list /
Price breakdown by merchant
CPU: AMD FX-6300 3.5GHz 6-Core Processor (€99.90 @ Caseking)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler (€36.49 @ Amazon Deutschland)
Motherboard: Gigabyte GA-970A-UD3P ATX AM3+ Motherboard (€82.58 @ Amazon Deutschland)
Total: €218.97
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-09-21 11:24 CEST+0200
and I would want about 50W more on my PSU.
For an overclocked FX 8
PCPartPicker part list /
Price breakdown by merchant
CPU: AMD FX-8320 3.5GHz 8-Core Processor (€139.90 @ Caseking)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler (€36.49 @ Amazon Deutschland)
Motherboard: Asus M5A97 EVO R2.0 ATX AM3+ Motherboard (€97.59 @ Home of Hardware DE)
Total: €273.98
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-09-21 11:25 CEST+0200
and now you need 50W more on your PSU.
For gaming, the 4460 will be equal to or superior to both AMD systems due to its more powerful cores, even if the AMD modules are substantially overclocked to much higher clock frequencies.