More details please, are you limited by temperature, will it post above 3.9, is 3.9 100% stable. Also what RAM do you have and have you tried adjusting the multiplier and if so what happens. Have you changed any settings other than the CPU voltage and the multiplier.
I am not limited by temperature acording to HWmonitor my procesor has 48-53 C I am using cooler master v8 processor cooler and extended ATX case with two 12cm fans at the top, one fan on the rear, one at the front and big 25cm fan on the side so cooling realy shouldnt be a problem. I am using two 4GB stick of team elite DDR3 1333 ram in dual channel mode (total 8GB) curently clocket at 1600 using a voltage of 1,65 volts ( stock is 1,50 volt). I reached 100% stable 3,9 GHz OC using multiplier at 19,5 and voltage of 1,47 volt. I also changed speed of PCI-express from 100 to 115 and speed of HT link from 2000 to 2400. At this setting my pc is completly stable.
OF COURSE!! Put RAM clock to the bare minimum, (and voltages to their default setting) then overclock the cpu to it's maximum, revert back 25-50 mhz when you reach the top, then start raising the RAM's clock to the max you can go with that cpu overclock.
You SHOULD get better results than just overclocking the cpu without touching RAM at all.
And DON'T TOUCH VOLTAGES!! It doesn't give anything potent and really damages your board faster than necessary. The theory for overclocking is as follow:
One shall lower voltages proportionally to the overclock achieved.
Though in these forums people tend to say the opposite... so if you can't overclock with stock voltages, then you shall NOT overclock that high. Every chip is different so everyone will get different results with the same chips...
Sorry for the uppercase but just preventing you from not seing these comments as it's pretty much the basics by now.
3.9ghz is not that bad so it's possible you won't get much higher, depending on your RAM's capability.
To start, drop your voltage to the lowest setting recommended for your processor. Overclock a step at a time, until you get to a point that is unstable. Bump your voltage until it is stable, and then continue overclocking. Wash and repeat until you either reach your comfortable level of overclock (heat, speed, etc.), or you have reached the maximum recommended voltage for your processor. Over-voltage your CPU at your own risk, as this is probably one of the fastest ways to ruin your kit (overheating being another). If you do this,though, you get the best overclock for the lowest voltage possible for your kit.
I tend not to worry about RAM clocks until I have a stable CPU overclock. Starting out, I keep the timings to the speed recommended for the memory as purchased For instance, if I bought DDR3 1333 9-9-9-24 rated memory, then at a minimum, I expect that memory to run at that speed no matter what my CPU clock is set at. Once I achieve a stable CPU overclock, I will then try to overclock the memory.
Tricks to a good overclock:
1) Buy your kit accordingly. Sometimes the most expensive processors aren't necessarily the best for overclocking. The idea is to get the most bang for your buck, so going out there and buying a $1000 CPU is not nearly as good for overclocking as it is to buy a $200 CPU and get within 90% of the processing power of the $1000 part through overclocking. CPUs that have unlocked multipliers are expected to be overclocked, but sometimes you can get good results from CPUs that don't have unlocked multipliers, since they can be bought for a bit less money and you can still wrench the same kind of performance as you can from the more expensive part.
2) Splurge on good cooling. You don't have to watercool, since most processors do well on air cooling alone, but the great thing about watercooling is that you usually only have to make the big investment once and then just keep upgrading your kit accordingly.
3) Also, splurge on a good power supply. Why buy an expensive computer and stick it with a cheap power supply? Especially for overclockers where even slight fluctuations in voltages might make a world of difference, if you start with a solid base, you have a better chance of eeking out more performance.