You're good to Overclock, to reach 4.0Ghz I don't really think you need any voltage adjustment. Just try to give this a shot:
1. CPU Ratio (CPU multiplier) set it to manual. Since you want 4.0 GHz as the clock speed and the base clock is 100 MHz, We can put it 40x (The multiplier).
2. Base Clock Put it default to 100 MHz, for an i5/i7 Just change the Multiplier and that's all (Although in other processor such as Phenom II I would change the base clock)
3. Voltage settings should be left at default, unless you see some system instability, increase the Voltage by a bit
4. Power Saving Mode should be disabled
5. Boot up to windows
6. Run CPU stability such as Prime95 and check the temperatures. If it goes up to 80C, feed more Voltage (small only) or put the clocks down, although this shouldn't happen.
How long should i run it?