You can usually use the highest all core turbo multiplier of the chip when running an all core OC so for your chip it would be 23, try this and see if it works.If anyone can chime in to how I can improve this, please do. Ratio of 21 is the highest for this chip.
Is it now a case of increasing the BCLK until it fails to be stable?
If that didn't work then you could try overclocking but with turbo enabled but bear in mind it will boost higher so would need more voltage, you would need to set the multiplier to auto for this to work. Eg bclk 191 and multi to auto would give a 4ghz clock but when stressed the turbo would boost this to a 4.4 all core and up to 4.6 on 2 cores.