Morewine has a good white paper on oak (link below).
The toast level has more to do with what kinds of flavor profile is imparted into the wine, not necessarily the amount of oak.
http://morewinemaking.com/public/pdf/oakinfopaper09.pdf
Summing-up, some applicable generalizations of toast levels on oak:
• The lower the toast, the more tannins (“structure”) and lactones (“wood-like” and “coconut”) will be present in each of the oaks.
• The higher the toast, the more spice and smoke notes will be present
• The deeper the toast, the more deep the caramel tones will be (moving into butterscotch at medium plus).
• Vanilla will increase up through a medium-plus toast and then decrease with a heavy toast and char.
• American oak will be more aromatic, but French oak will give more structure (Hungarian will give less than the French but more than the American).
• The greater the toast level, the lower the lactones (“wood” and “coconut”) for all three woods.
Medium plus is the most complex of all of the toast levels, and the most popular. Depending on the wine being made, this may or may not be a good thing!