I think you are going to get answers in the .670-.690 range as far as chokes go. Sumtoy on here may be able to help you also, other choices are Indian Creek, Pure Gold, Star-Dot (if you can find one) Kicks (they don't want you shooting Hevi)
There are many choices, but if you are looking to buy a choke that seems to do well in most 835, I think .670 in a Pure Gold is what you are going to hear the most about from the fellas on here, it has proven itself in many of 835's.
Hope this helps.
Also i never did get around to getting the MagBlends. I have the #7's for now, but I am in the process now of switching to handloading.
Good luck!