I have a brace of 6906s and 5906s. I use the 6906 with the longer magazine with a mag adapter to fit the longer mags into the shorter butt frame. I usually carry only one extra mag. Some of the "kids" point this out to me(they usually have 2 or 3 extra mags). I tell them that when I started as a patrolman I carried a 6 shot .38 special and only 6 extra rounds in a dump pouch(more was prohibited as the chief did not like the "cowboy look" of all that extra ammo). This means that I have 4 more rounds in just the one mag than I packed entirely back in the day. Of course no one really believes that a police chief could be that stupid-LOL.
The 3rd generation Smith autos may be the best series of semi auto handguns ever built by antone-ever.
The 6906 shoots better (for me) than the 5906, I think it has to do with the compactness of the gun and the more weight further back in my hand, also the shorter sight redius seems to service my older eyes than a longer radius-but maybe its just me-but who cares they all shoot very well.