In Stone's "Decision-making in Medieval Agriculture," he defines the medieval agricultural experience as one weighted in economic marginalism. That bit--that the medieval agrarian economy was marginal and thus liable to collapse if every ounce of effort wasn't put into farming whatever they could produce--makes sense to me. But it's a very england-centric way of looking at it.
What about in other places in europe during the medieval period? Would the Tuscan countryside have been anything like an english medieval farm in either produce, labor, or technology?
Well, I would say that it's difficult if not impossible to really summarize agriculture over the period of a thousand years in just one large region -- farms in Kent and farms in Yorkshire are going to have differences in skilled labor availability, in markets, sometimes in law and in ownership -- to say nothing of two countries.
According to the abstracts I can find, Stone focused on the 14th and 15th centuries and on farms owned by the great landlords.
Also, I think you're misunderstanding the concept of economic marginalism. If agriculture required every ounce of effort or it would collapse, a complex economy such as England had would have been impossible.
If you are to compare the Mediterranean against England in the Middle Ages, you may want to read up on how techniques, such as the heavy plow, has influenced the two places and how they may relate to each other. I wrote a bit about this here.
All that said, you are asking about large geographical areas and a very long time span.
In the 12-13th century there were lots of agricultural treatises discussing the pros and cons of various agriculutural innovations and farm management. One of the biggest was using horses instead of oxen for ploughing. Horses are better, as they can substantially increase the yield of a farm and some parts of Europe made the transition relatively quickly, with the ratio of horses to oxen steadily increasing and regions like Paris and and Normandy being completely horse-ploughed by the 13th century. The agricultural scene in other places such as England however was dominated by other ideas such as those of Walter of Henley, who was less convinced, arguing that it cost more to feed and maintain a horse. The expensive initial investment in changing to horses proved unwelcome in England and they continued to use primarily oxen in ploughing for some time. I don't know about Italian farms specifically however.
Source: The Medieval Machine, Jean Gimpel