I'm pretty sure the only difference is the barrel diameter.
The 835 has the big overbored barell, it's bored to 10 gauge specs. for the 12 gauge gun (.775 instead of .731).
The 535 has a standard size (bored .731) barell.
The bigger barell on the 835 is supposed to give a supperior pattern and lessen recoil.
But the smaller barell on the 535 gives you a lighter and more manuverable weapon.
This is my opinion, I'm not positive on it though.