You will have to wiggle that out yourself, as each chip has it's own characteristics. Might be somewhere between 1.15-1.3v for 4.4ghz. I'd start with 1.25v, if it's stable go down in like 0.01v steps until you are not stable anymore, then set it 0.01v higher again so you are stable. If you are not stable with 1.25v up the voltage in 0.01v steps until you are stable.
When you need less then 1.25v for 4.4ghz chances will be good that you can reach 4.5-4.6ghz. Usually 100mhz increases will only need a very tiny adjustment in voltage, once you need a lot more for a step of 100mhz I'd go back.
So for example if you need 1.25v for 4.4ghz but 1.32v for 4.5ghz, you should stay at 4.4ghz. If you can get 4.4ghz with 1.25v and 4.5ghz with 1.26v you can try to up until you need a lot of voltage increase for the next 100mhz. I'd personally stay below 1.3v, even if temperatures are fine.