I'd agree panel 6 would have bigger impact as a larger panel if that's the pay off reveal. But a smaller Unicron could work too. Revealing the shape and identity is all that matters.

The flow of text in panel 5 is off. My eye wants to reads the two Unicron speech balloons first rather than the first than jumping to the far right and back again to the left. I'd suggest Panel 5 has a split down the middle with one bubble from each character in each half.