In all honesty, your first plane. Use the supplied plastic push rods. You will likely never notice the trim difference when temps change. If you use metal rods, bushings of some sort (usually plastic and not metallic) or the outside plastic tubes from those supplied should be used to prevent the rod from bowing under presure. In this case 2-56 is sufficient for 40 size or smaller planes.

Once you get to the stage of more precise flight (plane 2 or 3) then start worrying about more precise set-ups.

Good Luck