http://www.youtube.com/watch?v=EL3-GpZQdS4
Watch n' learn m8 
Not sure which part it is in though, but watch all of it anyway, 'tis great!
Watching this whole thing...
I am disappointed.
Yeah, there are some times where they Held their spears in overarm position when standing in formation, But man did they have absolutely no striking distance when they did. I laughed.
However, when actually doing mock fights you see them using underarm style, just lifting their arm into position.
Yeah, Good argument bro. Overarm use of spear is bad when in formation. It is a damn fact. It does however look really heroic and manly to see overarm spear usage when not in formation -- as you will see on pottery and such. Pottery designed to sell. Not to be accurate depictions of battle. That is like saying you go and watch war movies like rambo to know how soldiers actually fight. Good logic.
If you want to stab from above, you just raise your arm and stab. You don't switch the grip and cut your spear length in half. Hell, you can even raise it to head level and still thrust under arm with all your length.
