If your cpu cooler is good enough to keep the FX 8320 cpu cool enough then 4.3 Ghz is going to be the max stable over clock you can get out of a FX 8320 cpu.
The average is from base clock speed yours being at 3.5Ghz if memory serves me right.
Is about 800 Mhz over clock frequency added to the stock setting at 3.5Ghz the chip works at factory default settings.
A small increase of the cpu`s vcore may have to be applied to keep the cpu stable at that frequency.
Where the temps of the cpu may rise so it is important you have a good air cooler or a AIO water cooling loop.
In order to test if the cpu is stable in windows and when put under any kind of cpu load you should run a prime 95 test.
keeping a very close eye on the cpu temps.
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