"These minions play plenty loud enough for me and my room. Is the only real advantage of using the tempests for my fronts in the 50-80hz range ? Minions crossed at 80hz. Otherwise would 100 to 15k hz range sound very similar between minion and tempest ?"
not entirely sure what the conditions were for the measurement. looks like it drops 6db vs. a 2pi space model starting around 100hz or so, not quite a 4 pi space model. in a room and/or near a wall(s) the bottom end response would be closer to the green line.
it would be nice if the cab tuning was specified on the website, otherwise its kind of model and guess.
that driver is quite capable, so if my model/guess is accurate (55hz tuning), it shouldn't run out of xmax until about 111db at 80hz, which is the -6db point for the crossover anyway, so that gives a total system capability of 117db or so, but you'd need more power than a typical receiver to get that high. it is only about 91db 1w1m in 2 pi space around 100hz, so 100 watts gets you 111db assuming no compression. that's pretty good, but not "rock concert" levels.
that is where the higher sensitivity of the tempest comes into play. it is about 97db sensitive in the same region. 6db is a fairly significant difference.