the 120 plannar macro is a great over all lense. but the unique point of this lense is that it is optimized as well for the close focus distance. i think that this is one among three lenses i know of this kind (the others are - the apo-ronars from rodenstok and the leica m 90 macro). this plannar is one of the best lenses.
the 80 plannar is not optimized for such thing. so the quality will not be up to the 120mm macro. but there is another differance - the field of view. the 80mm is wider one.
so.. if u want the best quality in the close range than it is the 120mmmacro. if u want wider and dont need the best quality etc than u can use the extenssion.
the 135mm lense is not femiliar to me at all.

note - the plannar 80 in my opinion is among the best lense u can have, but it is not really optimized for the close ups.