The most incredible thing I have EVER seen was the Vulcan flying testbed for the Concorde engines.
It had a full 2-engine Concorde nacelle in the bomb bay, live obviously.
The 2 Concorde engines, Olympus's like the Vulcans, were later much more powerful versions, together producing as much thrust as the 4 in the wings.
We saw it do its "party trick" at an airshow, but from behind. We were at, believe it or not the UK Prison Service annual dog show (don't ask, it's a long story...) which was about 2 miles from an airfield where the airshow took place.
The Vulcan flew very low and slow over us towards the airfield then put all 6 engines on full afterburners and literally went straight up, accelerating.
It was the noisiest, most indescribable thing I have ever experienced. Totally awesome, like I imagine a major earthquake to be.
The dog show was abandoned, the dogs were almost all uncontrollable afterwards.