I have both versions of the M3 (one of them is a pair of outdoor speakers). Admittedly, I haven't compared them A/B, but I've found no noticeable difference in everyday listening, across different music genres.

From what I understand, the biggest differences can be heard on the M80 and the QS4 (which now uses the 1" tweeter--the original had a 0.75"), although Alan would be the one to verify this.