The best setting you're not using in Build 42...

Set sprinters spawns to 1%.

This has brought so much tension back to the game for me. It's rare enough that you don't run into one very often. But when you do, it's absolutely terrifying because you're not expecting it. Plus, it makes taking on big hordes even scarier because you know there may be two or three sprinters in there, and you have to be ready to deal with them.

Highly recommended. I don't like playing with sprinters normally, but 1% is such a perfect sweet spot.