RE: Moss 835 Question...
In my opinion that choke is THE BEST factory choke on the market. With the right load it can be just as good as the high dollar chokes. I used to have an 835 and I eventually bought a Star Dot for it that held a tighter pattern than the factory choke, but not by much.
If i were in your situation, I would go out and buy a box of the 3.5'' or 3'' Winchester Xtended range 6's and give them a shot before you change chokes.