[AdamHeard]

Increasing the screw size increases the mechanical advantage which will help it stay in tension better, and will obviously have stronger threads. Stronger threads makes them less likely to wear out.

I'd just suggest 1/4-20 or 1/4-28, I'd also buy a solid rod end or clevis rod end and use that rather than the custom piece you have (lile 6071K41 on mcmaster). It'll save time and eliminate machining ops.