Hi just check in BIOS that FAN is Not on "Silent" or something like that profile.
FX series have lower threshold of max temp than other somewhere in 70C range.
i am @ 4.5 GHz stable since way too long.... on a Gigabyte MB. they should not have trouble overclocking....4.3 is nothing i can go 4.5 without any manual voltage tweak, i let the settings on auto in BIOS, and can go 4.8 without any voltage tweak on 2 modules 4 cores. Check PSU and if your system is already straining the PSU to the limit then it may be difficult.
And the temperature of VRM and other motherboard component is important too , hope you have well ventilated PC case.
Check following guide:http://www.overclock.net/t/1348623/amd-bulldozer-and-piledriver-overclocking-guide-asus-motherboardhttp://i925.photobucket.com/albums/ad91/kiuske/Benchmarks/4.5%20cpu_zps0bae74nm.png