I hear what you say about flying heights, but from my house in Mid Devon (it seems like it's a turning point from the Exe Valley towards Dunkeswell) I can see C130s night flying from my lounge window.
The house is at 400' AMSL, and when sitting in my chair on the ground floor the a/c are below this height using the valleys as a standard route.
I would estimate flying heights of some of these a/c at around 300' AMSL/200' AGL in my area