X48 vs X38
http://www.anandtech.com/cpuchipsets...spx?i=3150&p=5
Our top screenshots show our initial results when pushing the CPU and memory to an 11x410 setting...
...The Premium board required 1.59375V for the CPU and 1.69V for the MCH while the Deluxe board required 1.64375V and 1.73V respectively
It seems like intel optimized the X48 revision for less voltage needs, hence much heat less. Even the CPU needed a lot less voltage than on the X38: 0.05v for CPU and 0.09 for NB

I'm feeling the X38 was released too early. Great chip, but not a good extreme overclocker. The X38 and X48 boards had same maximum overclock in the end, but with lesser voltage on the X48, it should be much more stable