With stock cooling I would not even attempt to OC your cpu. Get an aftermarket cooler for that - even a dirt cheap Hyper 212 Evo is miles ahead of intel's stock cooler and will allow a modest OC.
Also, nobody can tell you how much your CPU can OC or how much voltage it needs for a given clock. At best we can give you very rough estimates, but the only way to get that information with any accuracy is to test it yourself.