Well first I need to ask why the 3.5" round. 3 inch does the job just fine.
But saying that, do note I do own a 3.5 gun but don't buy 3.5" rounds.
I do own a 11-87 SP which is chambered for up to 3 inch rounds only which has helped me harvest many, many birds.
I repalced the 26" barrel with a 21 inch catelever barrel, mounted a 1.5 x 4 Nikon Monarch Turkey Pro scope, the black pad is a Buck Creek Monte Carlo neoprene stock add on, and a Hastings 0.663 extended choke tube. I shoot 3 inch Winchester Surpeme #4 and have for many years. The gun is patterned to 55 yards if needed which I used only once.
JW