Dale your figures are close to the mark but I would have thought a more typical weight arriving on that run would be much lower, say around 240 ton. With a Vref around 140 adding 80 kts up to FL250 would give a rough holding speed of 220 something. Don't have any charts in front of me but I would have thought buffet would pop up around 185kt.
Descending in V/S, turning and with a subtle A/T failure you could get into the brown stuff very quickly. The main thing is, they caught it. As for the injuries, the poor old F/A's are always at risk. The idiot passengers without seat-belts never cease to amaze me. I don't know how you fix that, apart from chaining them to the floor.
As for wake turbulence, I got rocked about quite badly after take-off in LHR by a 757. That aeroplane punches above its weight for some reason and I am still very wary of them.
I feel sorry for the tech Crew, can happen to anybody.