The terms Standard, Semi-dwarf and Dwarf may not mean the same thing to everyone. A good example is last year when I called a well known nursery asking about the trees they advertised as "standard." I found out that these trees were actually on MM111 rootstock, which nearly all of us on this forum refer to as semi-dwarf. MM111 is a good rootstock for many situations, but it doesn't make what I call a standard tree.
Also, MM111, B118 and M7 are all generally referred to as semi-dwarf. The first two are excellent for many applications, but M7 has been described as a "noxious weed" by some experts. A good number of trees planted on M7 will likely fall over at some point in their lives unless they are supported in some way. I've been told that if you buy a Franklin Cider apple from Stark Brothers right now that you have no choice of the rootstock - and it could come on M7 - which I would consider horrible.
On pears, a good and commonly used rootstock for many soils is the OHXF 87. It gives a semi dwarf tree. A good full sized rootstock is OHXF 97. I could be happy with either of those.