Is there a particular aspect of the perception of the Norse that you're curious about? I can talk about contemporary perception of the Norse by others, but that's not the same thing as an objective analysis of their "brutality"

I am a bit late to this question, but if you have any more specific questions (as was mentioned by /u/Steelcan909) I can definitely act as a secondary resource!

Something that I wanted to add to this discussion (that may or may not help directly answer your question), is the idea of nuance especially when dealing with primary source material created during the Viking age. This is largely true for any period and any variety of scholarship, however it is particularly pertinent when we are dealing with "objective" accounts of brutality. In addition to all of the other disclaimers and nuance we (as historians) already have to add in when trying to measure a quality such as brutality, we also have to consider the unique interconnectedness that existed with Viking settlements in the Viking Age. While your question mentions Viking age England, I wanted to offer this resource that refers to a battle in Viking age Ireland. The study that is linked goes into a network analysis of the names mentioned in the Battle of Clontarf, which is widely recalled in the primary source material as a battle between the Irish and the occupying Norse, wherein the Irish forces emerge triumphant.

The study linked attempts to examine it from a more critical lens, finding deep interconnectedness in alliances and families a supposedly "international" conflict. While it is far from an answer to your question, I do think it offers a great primer into some of the issues that emerge when analyzing the Viking age. Even when primary sources and accounts exist and describe qualities like brutality or ferocity, which would theoretically be great tools to utilize in order answer your question, there emerge unique problems in contextualizing source material.

Again, this is not intended to be an answer to your question, but I hope it offers a little introduction and nuance to think about before we get into your deeper (or more specific) questions!