Common misconception about energy drinks. Coffee has between 100-200 mg per (8oz) cup, and the 16oz "full throttle" energy drink on my desk only has 160mg. It's comparable to a single cup of coffee brewed on the strong side.http://www.math.utah.edu/~yplee/fun/caffeine.htmlhttp://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/caffeine/art-20049372
A 6GHz CPU can do a computation faster. If the later computations rely on the result of the first, two 4Ghz CPU's could end up slower than a single 6GHz CPU. This is also one reason why the workload a CPU can actually accomplish is variable.
It's not the right way to measure the performance. Would you say two cars going 50mph is the same as one car going 100mph? It's the same thing with CPU's. Two CPU calculating at 3GHz are not equivalent to a single 6GHz CPU.