Why the extra $4 for an essentially identical processor? What role does the wattage play here? Which one should I buy and why?
Thanks for any help you can provide.
This is a processor stepping. Its minor improvements made to the manufacturing process. As saint said, the 140 watt version is C2 stepping. The 125 watt uses the newer C3.
The C3 will perform better and use less power in almost all cases. But its only 8 months old, so some boards, even new ones, may need a bios update before it will run properly. The C2 will run out of the box on just about any new board. Something to consider if your inexperienced.