How much diff does board size make?

I'm moving from a 156 Rippey to a 159 Timeless. I wanted a stiffer board for more of a carving ride.

I know there are differences inherent to each board, but in general, what differences would i notice from size alone?

Generally yuo have to go a good 3cm or more to get a noticeable difference in the same board. In the situation, the Timeless is going to plow through the crud better as well as be faster. This is not only due to length, but also slightly added width, construction, flex, etc.