Really?
Seems strange to me.
At light weights, Vmcg is down around 131 knots or so, IIRC.
The speed comes up mightly quickly in the -500.
Now, having said this, I haven't operated the aeroplane to CAA performance limitations, so you could be right.
Cambridge (Marshals) is about this length, as I recall, and I've operated from there direct to North America, flap 22, with a 10 knot headwind for departure, no pax of course.
Now, if we look at the takeoff weight limitation, and the runway required...
Runway 11,000 feet, sea level, 25C.
No obstacles
Flap 14
Max weight, 510,000 pounds, which is also the max structural allowed.
Takeoff distance required, 10,700 feet.
Using flap 22 (which was not commonly used), the distance required is less, of course