Interesting conversation. I have a quick thought. Merlin said,

"As we do not know what quality of troops Byrhtnoth had on hand (mainly in terms of morale, the willingness to fight), and we also do not know the quality of a given Viking army, we must allow that these factors are key in his decision to fight then and there."

I agree somewhat. Thiudareik's post was also quite good. It is entirely true that we cannot make accurate assumptions given the evidence that we have. One can debate all that one likes, but we must rely on the evidence if there is to be any real work done.
But what of the records that we do have? We know the victors and losers of some major battles, and the general course of the wars of the time. Is that enough to tell the genral makeup or success of armies, including Viking armies? I know that much of a battle, in fact probably a huge part of any battle of this type is dependant on the topography of the battlefield. But it may seem logical to conclude that on flat ground many Viking armies were superior to their English counterparts as a whole by looking at their past performances.

Thoughts?