Hi Xavier-
Reference fluxivity is a signal of known and standardized magnetic magnitude which is used to calibrate the gain of the reproducer so that program level meters (VU or PPM) read some standard level, usually 0db. The recorder will be calibrated to record this same fluxivity. Thus, reference fluxivity is used indirectly to set the levels recorded on tape.
So knowing what reference flux the recording engineers at TP use has no bearing on how the tape plays back on our machines, and isn't a value that we need to consider. You and I can rest assured that the brains at TP are recording at the level which is perfect for the source (i.e. say, classical or jazz) and the type of tape used.
As for the question of why use SM468 when there are other tapes with higher output available, the type of tape needed depends on many, many, MANY factors besides output, and I certainly don't have enough knowledge to intelligently comment on that, except to note that it is a "high output" tape and according to USrecordingmedia is the most sought-after tape on the market today.
Does this help out?