Actually, I traded both of my 5906's after getting my 5943. IMO, the all SS full-size S&W 9mm's, like the 5906/5946 are way too heavy for the 9mm round. There's no recoil to tame, so the weight is just wasted IMO.
The 5943 and 3953 I have both came from the Suffolk Co. Sheriff's Department as unissued pistols. If you have a choice, I would highly recommend swapping over to the aluminum framed 5943 for your duty weapon. Your back will thank you for it! I was issued an SW40F, and I was happy to carry such a light pistol when I also had to pack two spare mags, two sets of cuffs, radio, expandable baton, OC, keys, flashlight and a medical glove pouch. With all your gear, plus the weight of your vest, every bit of weight you can save is a bonus. I swapped over from leather gear to nylon, too. It may not look as good, but it's sure more practical, and you don't get the "squeak, squeak" with every step!