Your not missing anything by getting the 20’s. I also wanted to get the 18’s. Thought they looked great with the duratracs and still do. Dealership had a carbon pro come in with the 18’s on it so I was excited to buy the truck and get the rims and tires I wanted.
After owning the truck for a month, wish I had the 20’s. It’s not that the noise is that bad at low speed, but more than I am use to. Don’t seem to notice it too much on the interstate. Plus while driving on wet pavement, I am continually wondering if the traction is going to be as good as a more conventional tread pattern. So far, no problems but can’t stop thinking about it.