Well, I just got back two days ago from vacation, drinking and crisping myself on the beaches of Connecticut and Rhode Island, and as I sober up and my skin rapidly returns to its natural ghoulish white I have slowly read this thread and have noticed some key errors which are repeated over and over here:
1)Bretonnia could/couldn't cut off our supply lines:
Either way you slice it this is nonsense. Medieval warfare didn't deal in supply lines. There was a reason why Medievals thought in terms of campaign seasons and that is because they plundered and foraged and needed to know when they could at least potentially count on there being the necessary raw materials. True, during the Crusades supply lines were often involved, but this was an exception, and for two reason:
a)They had sea access
b)They were in a desert and foraging was not a certain way to get supplies.
Even here, the Crusaders did not always have access to Italian shipping, and here they usually made do.
2)Bretonnia could/couldn't hold land
Vernichtungsgedanke, blitzkrieg, total war, all of these are primarily modern concepts. Medievals were not concerned with holding land. They were concerned with defeating armies. Once they defeated whatever armies were in the region, they then moved to fortify or build castles and then hunkered in for the next attack.
This would usually be at least months, waiting for the next campaign season, and could often take years when we look at political considerations. In any case, the land grabs that many of you are referring to have nothing to do with Medieval warfare.
Land grabs have everything to do with modern warfare where mechanized units and capitalist/commodities cultures are involved, but they have virtually nothing to do with Medieval warfare. Land might be the primary objective for political/economic/psychological/religious reasons, but only on rare occassions did holding land matter for military reasons, and here it would inevitably be for strategic reasons, and usually this would be decided before the battle if possible.
We simply have more men than the Bretonnians because we are a pre-modern, capitalist, bourgouis society with a "Whig-myth" understanding of liberty, whereas as they are Medieval and feudalistic
Now, if someone could cite fluff that Bretonnia was definitely smaller in terms of population then I would give you that part of this argument; however, without a direct fluff reference we cannot know that Bretonnia is necessarily smaller. Even with significantly higher infant mortality and a lower lifespan, pre-industrial nations are quite capable of maintaining adequate birth-rates and dynamic population growth.
Even the "Whig" history that most of you seem to subscribe to does not indicate that the Bretonnian peasant would not fight with vigour for his Lord. Although I do not subscribe to "Tory" histories of deference and ancien regime and more than I do to "Whig" liberal narratives of liberty and progress, nevertheless, conservative/reactionary historians such as J.C.D. Clark, Lord Elton, Peter Nockles and Gertrude Himmelfarb have shown how maliable the older formulations of Monarchy/Church/Parliament could be.
Jingoism knows no bounds and even today's modern peasant will fight unquestioningly for his/her master merely in the name of patriotism or a flag. Imagine the faith of the Medieval then?
In summary, then, some of you have argued that the "table top" experience of Warhammer is not a good indicator of who would win a war if these two nations fought one another. Those of you who have argued so have set forth a number of arguments which relate both to the "real warfare" and to the imaginary "Warhammer world". I bring up my insights not to argue that one side would or could defeat the other, but to suggest that real-life examples are not germaine here, and that Game mechanics should be primary. Even fluff should only be applied to when it is clear cut, as "real-life" is often difficult to apply and certainly requires a much, much, more sophisticated analysis than even I have given here.