I've seen them spread out truly vast distances. They're just ice crystals and they're pretty tough. Do a google.com search for "contrails". Flip the switch to "images". Go through the collection. Some of them are obviously more than a mile wide.
Most of the photos are taken of contrail formations close to the aircraft producing them though, but when I grew up in Flyover Country I could lay there in the lawn on a hot summer's day and see HUNDREDS of contrails ~ many as high as 35,000 feet. So how wide do you think they might have been?
The trick here is the APPARENT width of the contrail ~ going no further than the distance of the horizon, whether that's 62, 42, 35 or fewer miles. An Apparent width can be computed without reference to WIND.
I grew up in the Denver area and watched a few hundred myself. I would say less than half a mile before they simply got so thin they no longer looked like a contrail at all.