Iīm running the 0804 BIOS, but you have to remember that Iīm running the P5B motherboard with the i965 chipset, yours is a P5W with the i975 chipset. While there are probably not all that big differences, the BIOS versions certainly are different which means that you might have options there that I donīt have and vice versa. I checked the Asus site and a new BIOS version (1707) for your motherboard was released on Dec. 15.
Yes Everest always reads the actual cores a few degrees hotter than "total" CPU. Itīs a little confusing, and Iīm not sure if there are 2 or even 3 different sensors (one inside each core plus one on the heatspreader) or its just one sensor and Everest and the other programs calculate the temperature by adding/decreasing a certain amount of temperature to specific areas of the CPU. One thing is for sure, its not uncommon that sensors are not always perfectly placed and read higher (or lower) than they should. Unless you run into stablity problems, alarms or some other kind of thermal related problems, I wouldnīt worry too much about it.
One thing I would certainly look at is your MB temperature. My MB temperature is around 28-30C and all my previous MBs always had such similar temperatures as well. Based on that knowledge and experience 48C for MB temp is way too high and not very common. Iīm not sure where they place the MB sensor. I used to think they place them either on the north or south bridges but they usually get hotter than 30C, so I donīt think thats it but another area might be close to the CPU socket (or even the rear side of it). You might get a better answer for this one at http://www.xtremesystems.com/
, the people there usually know tons of details about overclocking and certain motherboards. They have also very informative tutorials.
Unless your ambient temperature is like 40-50C, I think your sensor is highly misplaced or broken, or the BIOS version that you have is causing a false temperature reading. While I didnīt find a note about a temperature bug, but there might be one and it should be affected/fixed by updating your MBs BIOS to a newer version. I would recommend a visit to the xtremesystems forums and ask around if other people experience similar high MB temp with the BIOS version that you have, or possibly even a RMA of the MB.