I have not heard the M50 but I have M3v4. I expect M50 to sound similar to M3 but with more bass. The M3v4 is far better than the M3ti but the M5 is better in every way. You'll hear the M3v4 and want to burn your old M60s like I wanted to burn my M80v2. Then you'll listen to the M5 and cry out "That! THAT'S what I MUST have!" M5 is that sweet spot in the Axiom line-up.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated