I used 7/16" for the sheets on my C&C 35. I'll never understand why some people (and owner's manuals) use big lines for their running rigging. Bigger lines cost more, they often don't run freely through the blocks and they weigh down your sails in light air. I was guided in my choice of line sizes by the cordage manufacturer's recommendations. IMO, they know their own products better than the writers of owner's manuals.