the difference in max temps would be at different positions, some quote max EGTs at the sensor, others quote max temp of the external sensor body etc.
the sensor uses a 18x1.5 thread, you can get bungs in mild or stainless pretty cheap off the net if you need them
datalogit can do more than min, max and average. if you know what your doing you can get the exact afr at any given time, load, rpm etc in several different ways. the graph function is actually very handy for knock as you can see exactly where on the map the ecu was reading when it knocked, i dont mean which cell, i mean exactly how far between 4 cells and what the timing was at the time. the cell the knock value pops up in isnt always the culprit due to interpolation, same goes for fuel.