Reviews I've read of the G Speed Pro often describe it as "polarized". I'm not sure what that means, but it seems like it would mean that the racquet feels like most of the weight is in the opposite ends of the racquet.
I certainly wouldn't describe the Extreme as polarized. It feels solid and well-balanced to me.
You would think the open pattern on the Extreme would make it a little more powerful and easier to produce spin, but the Speed got good ratings in both those categories as well.
I just figured the biggest differences were in how the weight was distributed through the racquet, since that is supposed to be the thing with Graphene...its strength allows the weight to be placed differently.
Still, can't help but be curious based on the nearly identical specs.