I was just toying around with flush mounted chokes yesterday. A factory full in Remington 870 supermag turkey/waterfowl and Carlson's extra full .710 in an 835. Shot Federal premium 3" #5 and 3rd. degree in the 870 with good results. The 3rd degree shot a little tighter pattern.
With the 835 and Carlson's choke I shot Federal premium 3" #5 and Winchester XX magnum 3" #6. I have gotten better results shooting the Flight Control wad through full chokes.
At 30 yards the XX #6 is like throwing a net out there.