What sepping is it? If it is an E0 (more likely) then 4Ghz+ shouldn't be too hard with around 1.36V max needed for 4Ghz stable I would say from what I have seen. Try overclocking forums if you get stuck like overclockers.co.uk, ocforums, and there are many more also with people who have similar setups who have good knowledge of overclocking.
Just don't rush into overclocking, and after you reach your goal clock speed it is always good to fine tune voltages so that your power consumption is kept to a minimum, with less heat and lower voltage and the cpu will live longer.