Think convenience and comfort - - -
Tom B., in answer to your initial question, no, never carried a 686 of any kind. Lots of other revolvers, though, including some longer barrels: 6" Colt Officers Model Match, an M29 and a couple of 1955 S&Ws (pre-mod 25.) Also a 5" mod 27. Comfortable enough in a high ride, but I am tall.
Unless you have a snap lock swivel drop holsters, it is uncomfortable to sit wearing a long revolver. I used to choose chairs without arm rests when wearing the long barrels. Not too bad in a car with bucket seats and no center console.
Your requirements include--
3. 38spl, 9mm or 45 cals only.
From this, I take it that you would not be able to use .357 mag cartridges in the Mod 686, even if you chose it.
You asked first about the 6" 686, so I deduce that you are not overly confident in your CZ75.
In your position, I would probably choose the Colt OP 4". It is comfortable to wear, even with a drop holster. It is heavy enough to handle the best +P .38 cartridges available. (I strongly prefer the Rem or Win 158 LSWCHP.) There's no worry about banging an adjustable sight out of alignment in a duty holster. Comfort, strength, convenience, and you wouldn't be giving up a great deal of power. Also--Nowadays, a man packing a wheel gun is frequently considered comfortable with his own abilities. Appearences and self-confidence DO count for a lot.
Unless you anticipate being set upon by more than one or two bad guys at once, and since you have no need to conceal your sidearm, I can see no particular advantage in choosing the CZ.
Best wishes with your new job.
Johnny