If we look at the TDPs of the 2 chips(4770 and the 7700k) they are 84 and 91 watts respectively. That means the 7700ks TDP is 12% higher. Is that a great percentage?
Like it's been stated, use fresh TIM(after cleaning old), make sure the pegs for the cooler line up on the mobo, and use a good monitoring program(I use CoreTemp myself). Lastly, but not least, if everything installs correctly, the worst that will happen, is the cpu will throttle a little. Don't do heavy duty stuff, don't benchmark, and don't Overclock, and you'll be fine.