With Ivy Bridge, up to around 90-95C is very acceptable. Keep in mind that Prime95 will put an unrealistic load on your CPU in the first place, so any real-world application will most likely never get your CPU that hot. If we were talking Sandy Bridge, however....I would definitely want to keep the temperatures under 80C.
Also, your CPU cooler has a very thin radiator, thus it won't provide the best cooling possible. However, I could definitely see you take your CPU to around 4.4-4.5Ghz within reasonable temperatures