Peter:
The Scorpion spins faster for the same voltage, which is why it'll work with four cells to the eFlight 32's five. The Scorpion is rated for over 1000W continuous output: you'll have to check on the eFlight 32, but it's probably more than the average of 460 that I'm getting, or possibly even the peak of 720.
Keep in mind that as the cell count goes up, the cell capacity that you need goes down. The amount of energy you need to draw from the pack is going to be pretty much the same for both motors, and the weight of a pack is largely dependent on how much energy it can store. Whether there happens to be a sweet spot in the selection of cells that's available at any given moment that makes a 5S pack heavier or lighter than a 4S pack is pure chance. The important thing to remember is that a 5S pack that can hold the same energy is not going to be 20% heavier than a 4S pack.
As an example, William's 3700mAh, 4S pack corresponds to a 2960mAh, 5S pack. A quick check on the Hobby King site coughed up a 3700mAh, 4S pack that weighs 545g, and a 3000mAh, 5S pack that weighs 527g. So for those two examples, you actually save weight by going to a 5S pack (don't take that as being a done-deal, all-the-time thing -- it's just a quick example).