Well, this "large satellite vs. small satellite" question is the absolute crux of the question. If I plan to use subs crossed over at 80 Hz. anyway, then theoretically, even an M2 with frequency response down to 70 Hz. should be good. If I want to abide by the rule of "roll the satellites off one octave above their -3dB point," then I'd need at least the M50 towers for an 80 Hz. crossover. To use a 60 Hz. crossover, I'd need the M80s.
The only reason I'd see to need that rule is if I were playing the speakers at maximum volume. At lower volumes, the absolute output capability should not be an issue. Despite this, my friend insists that the M80 is the minimum Axiom I should consider for my room (and he also encourages me to get the "high-power" woofers).
The cost rises rapidly as one ascends the Axiom model line, and at the $2K on up level, there is SERIOUS competition from other manufacturers' products. Cost is NOT the main concern for me, but if I'm to spend that level of change, I want the best option.
I like Axiom's philosophy of spending on the drivers & crossover, not the cabinet finish (unless the customer wants to go there). I do think that some of Axiom's options should be available for less (particularly the outrigger feet for the towers).
And finally, I want to hear some speakers with ribbon midranges & tweeters before I buy. Of "conventional driver" designs, though, the Axioms (and the Thiels) sound the best that I've heard.
My opinion is worth exactly what you're paying for it!