The mobile P4 will be around 50% more powerfull methinks. The Celeron 2.6GHz is about as powerfull as a P4 1.6A methinks.
You could go with a Pentium-M 1.7GHz, aka Centrino (Centrino name requires company to use Intel's wireless stuff, same CPU). Because the Pentium-M is based on more efficient technology, it should be nearly as fast as the mobile P4 2.3, yet use around 1/2 the power.
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