Hey buddy, welcome to THG.
I would say 3.4/3.5Ghz and you will start to see temps raise a bit. Just make sure it does not exceed 60c at load (under stress) and you will be fine. Use speedfan, HW monitor or everest ultimate to monitor temps.
On a side note, I would invest in an aftermarket CPU cooler, this way you don't have to worry about it =)