What does the stock cooler get you out of interest?
If you take it easy, around 4ghz. Though I would suspect the temps to be borderline.
As mentioned sandy is a relatively cool running set of chips. You should easily be able to get away with clocks as high as 4.5ghz on a decent £30 cooler. Any higher and you should really be looking at high end air or water
iirc I had my 2600K @ 4.6ghz with an arctic cooling freezer pro 13 hitting temps in the low to mid 70's. H80 @ 4.8ghz in the high 60's low 70's and now custom water @ 4.8ghz giving temps in the high 40's to low 50's.
Remember stress temps, especially in IBT will be a great deal higher than heavy gaming stress. When I had my H80 gaming temps would often be 15c or so lower than IBT temps.