The US Half Letter is only about .2 inches taller than the A5 at the expense of being almost .3 inches narrower.
I think in the case of this template, width is more valuable than length. The narrower your paragraphs, the choppier the writing can feel.
That said, the change can feel pretty minimal. It depends on the project!
Some tips for readability:
- Remember to keep sidebars short. No more than 2-4 lines. Avoid one-word lines.
- Try not to hyphenate words across lines.
- Embrace the paragraph. Multiple singular lines broken by space can feel disjointed. When that feels unavoidable, consider using lists or tables.