I have a standard Vinci, so I'm not sure how applicable my experience is vs the 3.5 super.
I have got the best patterns with a choke in the .650-.655 range, with regular lead and hevishot.
Sumtoy makes a great choke for these guns, I have pattern pics in the Benelli pattern pic subforums.
My Vinci shot best with a clean, oil free barrel. My best patterns were with 3" magblends and Sumtoy
.650 choke. The one piece barrel and receiver is great for keeping gun zero'ed, no play and no problem
when disassembling gun for cleaning. Don't get insect repellent on the comfortec rubber pieces, it will
eat them up quickly, I learned this the hard way, and those comb replacements are ridiculously expensive. I'm in the process of making a wood one so I don't have this happen again. Vinci is an under rated
gun, I've had mine for 10 years I think, and it's been 100% reliable through thousands of rounds in many different hunting conditions for all kinds of game and targets.