My personal take is that, as far as purely crisp mental clarity goes, just being able to think and focus and concentrate without feeling like your brain is even slightly "cloudy" or distracted, Power Drive is the one. And yes, although it has zero stimulatory effect, this actually helps workouts a little bit, though maybe not to a massive degree, but it's noticeable.
Spike, on the other hand, doesn't give me that "purity/clarity of thought" that Power Drive does, but it's kind of like a stimulant without the stimulatory effects, if that makes any sense. It just feels like energy in a bottle -- no jitteriness like caffeine or ephedrine, no vibrating, just energy. You no longer feel tired, sleepy, like you just want to sit down, etc. It's very good in that sense. Almost like having magically added an hour or two of sleep to your previous night's sleep.
Obviously, both of these could be advantageous to either a workout or a studying session.