First of all the G43 is one of their lower end boards and it surely has less power phases than the higher end models. I think it's a 6 phase board as compared to 12 power phases on the GD65. This could be a main contributing factor. Also for higher overclocks there are many other factors and settings in the bios. I can't remember as it has been over 6 months since I overclocked my CPU but I am a newbie overclocker and was able to get my 3770k to 4.8 stable on my Z77 Mpower.
The board could be limiting factor, the chip could be your limiting factor or else you could be the limiting factor. What I would do if I were you is google every single bios setting that you don't understand and that will give you a better understanding of if you need to leave it auto/default or change the settings.
Some few settings to look into would be short and long duration power limit, internal pll overvoltage, EIST, spread spectrum, vdroop, c state. Sorry it's been a while and I just woke up.
Originally Posted by taafe
Try changeing vcore voltage to 1.35v you defo need to increase the voltage
I have no experience with haswell but 1.35 seems extremely high for just 4.2 or so ghz.