Here's some hard data (YTD 2025-looking at the PowerBI dashboard right now) from my company. It's worth noting that this data is inclusive of all carriers (i.e. VS, BA, and AA too), but >50% of our annual travel spend globally is with United.

Average RT fare paid by city pair.

Chicago-London: $5,633
Newark-London: $5,299
Washington-London: $6,057

Here are a other "similar" routes where we have a strong enough sample size for comparison (>$100k in YTD total spend)...

Nashville-London: $7,223 (maybe not that similar as BA is the only carrier on the route)
Chicago-Amsterdam: $5,849
Newark-Paris: $5,358

In terms of booking lead time, our average ticket is booked 27 days before travel, with 40% of travel booked on less than 14 days notice.