My first 533-V reported CPU temps of ~ 50C idle up to 68C under full load. I tried everything from lapping, to adjusting the alpha, etc.
Got a new board (had an issue with the bios data not being saved when the system was removed from AC power), and now my temps are 37-41C idle, 48-55C load.
Same brand, same model, etc.
Either I was doing something wrong the first 5-6 times I tried applying arctic silver/lapping/adjusting, or the temp readings on m/b's aren't exactly accurate I honestly don't know that answer to that.
With a stock HSF, however, you're not going to get much cooler. In my experiences, the voltage and overclock hasn't made all that much of a difference in the temperature.