I also have a P4 1.8A on a TH7-II.
At stock speeds, my load is around 51-52C, and idle is around 43. I am using the stock heat sink and fan with AS3. I run it at 2.0Ghz, and the temp is 45C/53C Idle/Load. I stopped worrying about temp really.
Either the motherboards vary quite a bit on temp readings, or the P4's vary quite a bit. Some people have very low temps, and others have temps like mine. I have tried the thermal pad, and AS3. I think some people are getting the 1.6a/1.8a's that could have been sold as 2.4's but due to demand are marked to the lower speed... others are getting chips that would have normally only been rated as high as what you bought them as.
Critical temp on the P4 1.8's is 67 degrees. Sometime after that they will begin to throttle back. There is pretty much no chance in burning it up. It would take years for even a 65C temp to have any affect on the chip, and I doubt you plan on keeping it that long.