Should an Athlon under load be running at 55 degrees C? (I suspect not, perhaps the board really is providing 1.81 volts)

It is possible, as AMD's biggest problem with current chips is the heat generated. The 1.4 should be comming out with a new cooler running core, but it's possible they are going to try and stretch the existing core a bit more. I still remember the 1.0gHz slot A Athlon Gateway had as a prototype to train us onn. Massine heatsync, and a fan located directly above it, with the holes needed made into the side of the case. The origional core got really hot :-)

Here is a link showing the heat the newer ones are putting out http://www.anandtech.com/showdoc.html?i=1441&p=2