If i understand your measuring correctly, this is partial nonsense too.
You use impostors, not the landscape when the distance is greater than 500m or so.
The only situation in which landscapes irrevocably cauase perfromance issues is when you sit at the intersection of 4 of them and all of them are actually loaded in memory at rhe same time.
As such, you can benchmark your player’s worse possible performance by keeping 4 levels always loaded.
Thats your worse possible baseline.