Since I started simming in 2002 I have flown in Europe; the only times I flew in the US was the default airport just to check out a 'plane or a setting.
I recently flew a tutorial of a payware airliner into a major US airport and was amazed at the considerable drop in fps, even before lining up and having the airport in full view.
After a couple of 'experiments' (that's the word I use for 'mucking about') with default airports and a couple of payware demos I realised that the principal culprit is the surrounding autogen. There is just so much default a-gen around a typical large US airport compared to say, Rome, Madrid or Zurich that even before you take into account the fps hit of the airport itself, things are slowing down. On my (getting a bit tired and constipated) rig the difference is between high teens and low teens.
Has anyone else found this?