I guess that's the difference between a 'FS' pilot and a real pilot. Google "Indicated Airspeed" and "True Airspeed" and "Ground Speed" !
Hmmmm, the vast array of aircraft I fly on FS makes me most knowledgable, especially with varying flying characteristics; thus I know the Jumbo just as well as anyone who flies it. The airframe is simply not built to withstand speeds of 800mph. None of the airspeedometers in any of the jets I regularly fly (yes, it’s just the same as ‘real flying, all the dials work) go much beyond 550kts.
AND that aircraft on the treadmill WOULD take off. The thrust is pushing the wheels at 200 mph.