I'm thinking this is an understatement as the average Roman male was between 5'5"-7" and the native Britons of that era seem about the same.
Rome sucked out its military in the early 400s and was gone by 430. England's southeast coast already had fortification identified as "Saxon Shore" from the 200s but there is still a lot of controversy over how 'violent' the Anglo-Saxon incursions were in the period after Rome. Truly a 'dark age' with few records or chroniclers.
One thing noted in the article was how shallow the burial had become over time. After the mentioned 1,400 years, there would have been erosion and then near continuous agriculture. Kind of shows why these metal-detector enthusiasts do have successes, even when someone else has already 'worked' an area.
Thanks for an interesting post, SunkenCiv!
Saxon settlement dates back to the Roman Empire’s Crisis of the Third Century. The rebel emperor Carausius ruled northern Gaul and the province of Britain, and had the smarts to evacuate both his troops on the continent and the navy he controlled, moving it to Britain to keep it from being taken in a land attack.
http://www.google.com/search?q=carausius