If they are the same design, they should act the same, except for an increase in depth and
coverage generally in proportion to the difference in size.
Fer instance, my Ace 250 6x9, and my 9x12 are the same design, except one is bigger.
Being as on average, it's 3 inches larger, you can generally expect the pattern to be
2-3 inches deeper. So if I get 8 inches on something with the stock coil, I'll get 10-11
using the 9x12. And also cover that much more area per swing.
On the down side, the larger coil will see more of the ground at once, and in busy or
trashy areas could slow you down a tad as you weed through the clutter.
On the plus side, in clear areas, the big coil is going to cover more ground per hour,
and go deeper. I always use what fits what I'm doing. So I'm often swapping coils around.