i've pushed mine to 3.73GHz and still been very stable (temps around 60-65°C)... but it'll all depend on your particular board and how well you know how to set with the voltages (just make sure you have enough through the NB and core and you should be ok to get 3.25 or so)
to combat that core seperation problem, make sure you apply the paste VERY evenly, and make sure the cooler is seated evenly... my cores usually sit with about 3° difference at idle and load... so you're not doing to bad