I killed one several years back with 3.5'' #6 shot at 54 yds and thats a rangefinded 54 yds not a guestimate. They will do the trick for you with no problems at all.

I've shot them at 35 - 40 yds with 3" #6, but that's as far as I'll go. My choke is only a standard full. I've also killed them with #5 at this range, never lost one, but I switched to #6 to gain about 100 pellets over the #5.