I bought an A/B switch and I finally had a chance to set the V2 and V4 up side by side.
It wasn't an ideal test, the V2 location was jury rigged (sitting on top of the shipping boxes), and the V2 must have a higher SPL because they were 3 -6 db louder,.
But it didn't have to be ideal conditions because the differences were not subtle.
The sound stage, which Mojo asked about, was leaps and bounds better on the v4. And by better, I mean more precise location and better able to pick out instruments. On the other hand, the v2 gave more of a concert hall sound if that's your thing.
The high end was, as expected, also much, much better. I knew this already, but comparing A/B made it even more noticeable. Cymbals and cymbal brushes were noticeable on some tracks where they had been muffled or even buried before.
Of course, I still had my problem where I thought the v4 lost something. I even drug in my wife, who in a semi-blind comparison, also liked the v2's better.
I did some more playing around and I think I narrowed it down to mid-range performance. I think the v2 is much more pronounced in the mids.
To test this theory I set up a manual equalization exaggerating of the mid at +3.5 at 1k, and then outward from there at +3.0, and +2.0. (This is with a Yamaha RX-681.) Then I switched between the 681's 'natural' setting and my manual setting on both the v2 and v4's. On the v2 the difference was relative slight. On the v4, using my crude mid enhancement dramatically made the V4 sound more like the v2.
So I'm going to leave the v4's up and play around with a more precise mid boost.
Bottom line though, the M5's are the way to go for any future purchase. I'd be inclined to return the M22s if (1) I didn't need a hobby, (2) my location wasn't perfect for the M22's and (3) I didn't go out of my way to virtually hold my breath and say I wanted the M22's.
