Did you install the CPU paste right? is the cooler tightened down enough, Keep in mind the 4790k is probably one of the hottest CPU's on the market, but it should not be hitting this high
i would say try using a different stress testing program. prime95 is said to not be very good for newer intel cpus. im not sure how accurate that is, but i can tell you first hand it really cranks the heat up. try something like aida64 and see what you get. report back if you can.