Thats definitely hot heh. "technically" in the computer world, doing almost anything voids a warranty. But its almost impossible for them to tell. I wouldnt woryy about it to much. But yes, putting as5 on it will void the warranty. As well as using an aftermarket custom heatsink as well.
Are you ocing or something? Thats a very high temp. I would turn your stuff off and make sure the heatsink is on correctly. Or down all the way. AS5 isnt going to fix that temp down to where it should be. AS5 is only a minior decrease. If that doesnt work, I dont know what to tell you. Check the bios to see if it is at the correct voltage (my mobo has a problem with the right stock voltage)
I would almost say that the sensor is wrong by that temp. If the heatsink is attached correctly, and it doesnt feel that warm, might be a sensor problem.
Damn and I thought my 40C at stock was a problem.