im building a decking in the corner at the bottom of my garden. its 10ft each way with a stretched curve. im about to buy boards today. my question is do i buy 5inch to maybe give it an illusion of looking larger than it actually is or buy 6 inch for less fixing and cost, plus maybe stronger when cutting curve down its length. might fit lights into board if that makes any difference? this is my first attempt, i appreciate any advice!