Well, you've seen the pictures of the two bats. There is a noticeable difference in the volume of willow that each contains, although the masses are just 0.2oz apart.
But what of using them? In three parts:
Knocking in/tapping up with a mallet
Quite honestly, I couldn't feel a difference. Both have decent, long middles, both rebounded very nicely off the mallet. At this stage of the test, it's made next to no difference.
Use against a Bola
Again, both are good bats, both pressed slightly differently, but to me and the others who used them, no discernible difference when middling one, and very little difference in sweet spot coverage, only down towards the toe, where shape will make the difference.
Use against real cricket balls
This is the one that everyone really wants to know. How do the two bats compare against real cricket balls. This has been done in two ways. Hitting thrown balls and facing bowlers. In neither was I able to categorically state that one performed better than the other. There felt like no difference between the two. Both are decent grade willow, both are pressed well according to the characteristics of the cleft, and both hit cricket balls in a way that, if you're a good batsman, will score you runs.
Conclusion
Here's what you've all been waiting for.
The size of the bat doesn't matter!
While this may be very disappointing to many people, the basic physics of it are that, for properly pressed willow, a mass is moving in one direction, impacting a mass moving in the opposite direction. The change in force is related for the most part to the speed and the mass directly, followed by the characteristics of the material.
As the mass and bat speed play the greatest part, whether the willow is high or low density makes next to no difference, as the physical characteristics of willow are common. If it is pressed sub-optimally, I have no doubt that there will be an impact on performance, and likewise, a laminate is changing the physical characteristics of willow, so may change the performance. Density, though, really makes no physical difference to what you wield.
The only good reason I can give for people hitting better with larger bats is that they inspire confidence in a different way.