Would a 2.6 Ghz CPU drain a laptop's battery faster than a 2.3 Ghz CPU?
If everything else was equal (CPU architecture, generation, manufacturing process, OS, power management strategy, software running etc.) the answer is maybe. Modern CPUs like the i3/i5/i7 series downclock themselves when idle so it depends what you're doing and what the actual CPUs are. If everything is as equal as you can make it and you compare CPUs of identical generation, one with maximum clock speed higher than the other and you are using the CPUs to their maximum capacity - then the more powerful CPU does drain the battery faster - but it gets more work done in the same time too, and might get back to the idle state faster. 

You can only really answer this question if you test your exact scenario.